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Linked servers are now simulated by linking separate Simulation instances.
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‎CLAUDE.md‎

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@@ -4,7 +4,7 @@ Auto-loaded orientation. `README.md` is for humans.
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## Identity
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`SqlServerSimulator`: in-process .NET 10 SQL Server simulation. It's an **ADO.NET stand-in for `Microsoft.Data.SqlClient`** — consumers create a `Simulation`, get a `SimulatedDbConnection` via `CreateDbConnection()`, and use it with (for example) `Microsoft.EntityFrameworkCore.SqlServer` instead of going through SqlClient over the wire. Public surface is `Simulation` + `CreateDbConnection()` + `SimulatedDbConnection` (subscribers for `InfoMessage` + supporting `SimulatedInfoMessageEventArgs` / `SimulatedError` / `SimulatedErrorCollection`); `QualityTests.PublicApiWhitelist` fails the build if anything else leaks public — resist expanding.
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`SqlServerSimulator`: in-process .NET 10 SQL Server simulation. It's an **ADO.NET stand-in for `Microsoft.Data.SqlClient`** — consumers create a `Simulation`, get a `SimulatedDbConnection` via `CreateDbConnection()`, and use it with (for example) `Microsoft.EntityFrameworkCore.SqlServer` instead of going through SqlClient over the wire. Public surface is intentionally minimal so internals stay free to refactor; `QualityTests.PublicApiWhitelist` is the authoritative list and fails the build on any unintended expansion — resist adding to it.
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`SqlServerSimulator.EFCore` is a sibling package whose only public method is `UseSqlServerSimulator(DbContextOptionsBuilder, DbConnection)`. EF Core's SqlServer provider keeps emitting SQL-Server-flavored SQL; the adapter just registers an `IRelationalTypeMappingSourcePlugin` for the (CLR, store) pairs whose default mappings downcast to `SqlParameter` (since the simulator's connection isn't a `SqlConnection`).
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@@ -172,13 +172,15 @@ Per-feature deep-dives live under `docs/claude/`. Each entry below is a trigger:
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- **`ALTER DATABASE SET <option>` accept-list + `COLLATE` clause** → [`database-options.md`](docs/claude/database-options.md).
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- **New top-level statement parser or dispatch-loop separator rules** → [`grammar.md`](docs/claude/grammar.md) + [`control-flow.md`](docs/claude/control-flow.md).
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- **BACPAC import** (`Simulation.ImportBacpac` instance method — multi-database via repeated calls, `BacpacImportOptions`, `ModelXmlReader` dispatcher, BCP wire format, `BacpacBuilder` test harness) → [`bacpac-loader.md`](docs/claude/bacpac-loader.md).
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- **Linked servers** (`Simulation.AddRemoteSimulation`, `sp_addlinkedserver` / `sp_dropserver`, four-part-name FROM routing through the remote's ADO.NET pipeline, `sys.servers`) → [`linked-servers.md`](docs/claude/linked-servers.md).
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## Not modeled
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- **Key-range locks** — sole remaining phase 4+ deferral. See [`locking.md`](docs/claude/locking.md) for what does ship (full 8-mode matrix, SNAPSHOT/RCSI, DMVs, Msg 1205/1222/3952/3960).
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- `BEGIN DISTRIBUTED TRANSACTION` raises `NotSupportedException` at dispatch. `BEGIN TRANSACTION <name> WITH MARK 'm'` raises **Msg 319** at parse (the parser doesn't accept `WITH` here); bare named transactions (`BEGIN TRAN t1`) ship.
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- **`CREATE DATABASE`** / **`CREATE ASSEMBLY`** — Msg 102 at parse. Adding databases routes through `Simulation.ImportBacpac`; CLR assemblies aren't modeled at all.
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- **Cross-database DML** (`INSERT`/`UPDATE`/`DELETE`/`MERGE` through a 3-part name targeting a different database) raises `NotSupportedException` via `BatchContext.RejectCrossDatabaseMutation` — trigger scope swapping, identity allocation routing, undo-log scoping, FK validation across DB boundaries pending. Issue `USE <db>` and reference via a 1- or 2-part name. Cross-database SELECT / JOIN / catalog-view reads (`SELECT * FROM other.dbo.t`, `dbA.sys.tables`) ship. **Four-part `linkedserver.db.schema.t` names** surface as Msg 208 instead of real SQL Server's Msg 7202 (no linked-server model). See [`schemas.md`](docs/claude/schemas.md).
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- **Cross-database DML** (`INSERT`/`UPDATE`/`DELETE`/`MERGE` through a 3-part name targeting a different database) raises `NotSupportedException` via `BatchContext.RejectCrossDatabaseMutation` — trigger scope swapping, identity allocation routing, undo-log scoping, FK validation across DB boundaries pending. Issue `USE <db>` and reference via a 1- or 2-part name. Cross-database SELECT / JOIN / catalog-view reads (`SELECT * FROM other.dbo.t`, `dbA.sys.tables`) ship. **Four-part-name writes** (`linkedserver.db.schema.t` INSERT/UPDATE/DELETE/MERGE) also raise via the same factory — see linked-servers below. See [`schemas.md`](docs/claude/schemas.md).
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- **Cross-server writes** through four-part names raise `NotSupportedException` (lock-manager + undo-log coordination across `Simulation` boundaries pending; parallels the `BEGIN DISTRIBUTED TRANSACTION` stance). **Four-part-name reads** ship through the remote `Simulation`'s full ADO.NET pipeline. See [`linked-servers.md`](docs/claude/linked-servers.md). **Catalog views through four-part names** (`srv.db.sys.tables`) currently fall through to Msg 208 — issue catalog queries against the remote `Simulation` directly.
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- **`SET <option>` accept-list** (`Simulation.Set.cs`) covers XACT_ABORT, all ANSI/session-state toggles, `STATISTICS {IO|TIME|XML|PROFILE}`, value-taking options (`TEXTSIZE`/`DATEFIRST`/etc.) — all parse-and-discard. Unknown SET → Msg 195. `SET @v`, `IDENTITY_INSERT`, `NOCOUNT`, `LOCK_TIMEOUT`, `TRANSACTION ISOLATION LEVEL` carry semantic effect.
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- **`ALTER DATABASE … SET` / `COLLATE` surface** — see [`database-options.md`](docs/claude/database-options.md). Most options parse-and-discard; `COMPATIBILITY_LEVEL`, `ALLOW_SNAPSHOT_ISOLATION`, `READ_COMMITTED_SNAPSHOT` are load-bearing.
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- `RANGE BETWEEN <N> PRECEDING/FOLLOWING` numeric-offset — Msg 4194, matching real SQL Server's licensed-feature rejection. `ROWS` numeric-offset ships. Default frame with ORDER BY is `RANGE UNBOUNDED PRECEDING TO CURRENT ROW`; without it, whole partition. LAST_VALUE matches real SQL Server's default-frame semantic.

‎SqlServerSimulator.Tests/LinkedServerTests.cs‎

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using static Microsoft.VisualStudio.TestTools.UnitTesting.Assert;
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namespace SqlServerSimulator;
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[TestClass]
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public class LinkedServerTests
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{
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/// <summary>
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/// Two-step registration: <c>AddRemoteSimulation</c> binds the name, but
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/// the linked server isn't reachable from SQL text until
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/// <c>sp_addlinkedserver</c> activates it. A four-part reference before
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/// activation surfaces as Msg 208 (matches the simulator's existing
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/// behavior for unknown linked servers — Msg 7202 isn't ported).
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/// </summary>
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[TestMethod]
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public void FourPartName_BeforeSpAddLinkedServer_Msg208()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.remote_t (id int not null primary key, val int not null); insert remote_t values (1, 10), (2, 20)");
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.AssertSqlError("select val from OTHER.simulated.dbo.remote_t where id = 1", 208);
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}
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[TestMethod]
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public void Select_RoutesToRemoteSimulation()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.remote_t (id int not null primary key, val int not null); insert remote_t values (1, 10), (2, 20)");
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver @server = 'OTHER', @srvproduct = 'SQL Server'");
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AreEqual(20, local.ExecuteScalar("select val from OTHER.simulated.dbo.remote_t where id = 2"));
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}
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/// <summary>
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/// Positional sp_addlinkedserver form: real BACPAC scripts emit
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/// <c>EXEC sp_addlinkedserver 'OTHER', 'SQL Server'</c>. The simulator
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/// accepts both forms.
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/// </summary>
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[TestMethod]
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public void SpAddLinkedServer_Positional_Activates()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.remote_t (id int not null primary key); insert remote_t values (1), (2), (3)");
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER', 'SQL Server'");
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AreEqual(3, local.ExecuteScalar("select count(*) from OTHER.simulated.dbo.remote_t"));
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}
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[TestMethod]
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public void Join_AcrossLinkedServer()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("""
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create table dbo.parts (part_id int not null primary key, name varchar(20) not null);
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insert parts values (1, 'widget'), (2, 'gadget'), (3, 'gizmo')
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""");
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var local = new Simulation();
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_ = local.ExecuteNonQuery("create table dbo.orders (order_id int not null primary key, part_id int not null, qty int not null); insert orders values (1, 1, 5), (2, 2, 10), (3, 1, 7)");
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local.AddRemoteSimulation("PARTSRV", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'PARTSRV', 'SQL Server'");
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var qty = local.ExecuteScalar("""
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select sum(o.qty)
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from dbo.orders o
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inner join PARTSRV.simulated.dbo.parts p on p.part_id = o.part_id
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where p.name = 'widget'
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""");
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AreEqual(12, qty);
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}
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[TestMethod]
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public void Insert_ThroughFourPartName_Rejected()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.remote_t (id int not null primary key)");
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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var ex = Throws<NotSupportedException>(() => local.ExecuteNonQuery("insert OTHER.simulated.dbo.remote_t values (99)"));
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Contains("Cross-server write", ex.Message);
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}
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[TestMethod]
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public void Update_ThroughFourPartName_Rejected()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.remote_t (id int not null primary key, v int not null); insert remote_t values (1, 1)");
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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_ = Throws<NotSupportedException>(() => local.ExecuteNonQuery("update OTHER.simulated.dbo.remote_t set v = 2 where id = 1"));
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}
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[TestMethod]
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public void Delete_ThroughFourPartName_Rejected()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.remote_t (id int not null primary key); insert remote_t values (1)");
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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_ = Throws<NotSupportedException>(() => local.ExecuteNonQuery("delete from OTHER.simulated.dbo.remote_t where id = 1"));
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}
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[TestMethod]
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public void SpAddLinkedServer_Unregistered_NotSupported()
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{
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var local = new Simulation();
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var ex = Throws<NotSupportedException>(() => local.ExecuteNonQuery("exec sp_addlinkedserver 'NOT_REGISTERED'"));
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Contains("AddRemoteSimulation", ex.Message);
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}
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[TestMethod]
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public void SpDropServer_RemovesLinkedServer()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.t (id int not null primary key); insert t values (1)");
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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AreEqual(1, local.ExecuteScalar("select count(*) from OTHER.simulated.dbo.t"));
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_ = local.ExecuteNonQuery("exec sp_dropserver 'OTHER'");
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_ = local.AssertSqlError("select count(*) from OTHER.simulated.dbo.t", 208);
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}
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[TestMethod]
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public void SpDropServer_Missing_Msg15015()
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{
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var local = new Simulation();
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local.AssertSqlError("exec sp_dropserver 'NOT_REGISTERED'", 15015,
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"The server 'NOT_REGISTERED' does not exist. Use sp_helpserver to show available servers.");
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}
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[TestMethod]
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public void SpServerOption_ParseAndDiscard()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.t (id int not null primary key); insert t values (1)");
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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_ = local.ExecuteNonQuery("exec sp_serveroption @server = 'OTHER', @optname = 'data access', @optvalue = 'TRUE'");
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_ = local.ExecuteNonQuery("exec sp_addlinkedsrvlogin 'OTHER', 'false', NULL, 'sa', 'password'");
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AreEqual(1, local.ExecuteScalar("select count(*) from OTHER.simulated.dbo.t"));
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}
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/// <summary>
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/// The remote SELECT must run through the remote's full pipeline — its
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/// catalog views resolve at the remote, not against the local
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/// Simulation's catalog. Verified by reading sys.tables on the remote
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/// via a four-part-name reference; if the routing accidentally bound
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/// against the local instance, the row count would differ.
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/// </summary>
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[TestMethod]
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public void RemoteSelect_RunsThroughRemotePipeline()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.a (id int); create table dbo.b (id int); create table dbo.c (id int)");
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var local = new Simulation();
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_ = local.ExecuteNonQuery("create table dbo.only_local (id int)");
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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// Verify remote-side data is what arrives, not local-side.
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AreEqual(3, remote.ExecuteScalar("select count(*) from sys.tables"));
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AreEqual(1, local.ExecuteScalar("select count(*) from sys.tables"));
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}
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/// <summary>
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/// Self-linkage: a simulation can register itself as a linked server.
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/// Useful for tests that want to exercise the round-trip code without
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/// constructing a second Simulation.
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/// </summary>
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[TestMethod]
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public void Selflink_RoundTrip()
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{
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var sim = new Simulation();
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_ = sim.ExecuteNonQuery("create table dbo.t (id int not null primary key); insert t values (42)");
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sim.AddRemoteSimulation("SELF", sim);
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_ = sim.ExecuteNonQuery("exec sp_addlinkedserver 'SELF'");
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AreEqual(42, sim.ExecuteScalar("select id from SELF.simulated.dbo.t"));
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}
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[TestMethod]
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public void SysServers_LocalOnly()
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{
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var sim = new Simulation();
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AreEqual(1, sim.ExecuteScalar("select count(*) from sys.servers"));
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AreEqual("SIMULATED", sim.ExecuteScalar("select name from sys.servers where is_linked = 0"));
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}
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[TestMethod]
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public void SysServers_ProjectsActiveLinkedServers()
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{
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var remote = new Simulation();
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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local.AddRemoteSimulation("THIRD", new Simulation());
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver @server = 'OTHER', @srvproduct = 'My Product', @provider = 'My Provider', @datasrc = 'My Source'");
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'THIRD', 'SQL Server'");
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AreEqual(3, local.ExecuteScalar("select count(*) from sys.servers"));
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AreEqual(2, local.ExecuteScalar("select count(*) from sys.servers where is_linked = 1"));
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AreEqual("My Product", local.ExecuteScalar("select product from sys.servers where name = 'OTHER'"));
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AreEqual("My Provider", local.ExecuteScalar("select provider from sys.servers where name = 'OTHER'"));
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AreEqual("My Source", local.ExecuteScalar("select data_source from sys.servers where name = 'OTHER'"));
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}
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[TestMethod]
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public void FourPartName_ToRemoteCatalogView_FallsThroughToMsg208()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.t (id int)");
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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// Catalog views aren't reachable through four-part names yet; the
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// lookup misses because sys.tables isn't a HeapTable in the remote's
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// schema dict. Falls through to Msg 208 — documented gap.
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_ = local.AssertSqlError("select count(*) from OTHER.simulated.sys.tables", 208);
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}
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[TestMethod]
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public void FourPartName_MissingRemoteTable_Msg208()
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{
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var remote = new Simulation();
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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_ = local.AssertSqlError("select * from OTHER.simulated.dbo.no_such_table", 208);
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}
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[TestMethod]
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public void Merge_ThroughFourPartName_Rejected()
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{
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var remote = new Simulation();
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_ = remote.ExecuteNonQuery("create table dbo.remote_t (id int not null primary key)");
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var local = new Simulation();
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_ = local.ExecuteNonQuery("create table dbo.src (id int not null)");
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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_ = Throws<NotSupportedException>(() => local.ExecuteNonQuery("merge OTHER.simulated.dbo.remote_t as t using dbo.src as s on s.id = t.id when matched then delete;"));
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}
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/// <summary>
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/// Reactivating an existing linked-server name replaces the prior
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/// binding silently — matches real SQL Server's <c>sp_addlinkedserver</c>
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/// idempotency. Useful for BACPAC scripts that re-emit registration
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/// on every import.
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/// </summary>
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[TestMethod]
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public void SpAddLinkedServer_Idempotent()
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{
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var remoteA = new Simulation();
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_ = remoteA.ExecuteNonQuery("create table dbo.t (id int); insert t values (1)");
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var remoteB = new Simulation();
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_ = remoteB.ExecuteNonQuery("create table dbo.t (id int); insert t values (2), (3)");
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var local = new Simulation();
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local.AddRemoteSimulation("X", remoteA);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'X'");
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AreEqual(1, local.ExecuteScalar("select count(*) from X.simulated.dbo.t"));
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local.AddRemoteSimulation("X", remoteB);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'X'");
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AreEqual(2, local.ExecuteScalar("select count(*) from X.simulated.dbo.t"));
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}
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[TestMethod]
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public void SysServers_RemovedBySpDropServer()
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{
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var remote = new Simulation();
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var local = new Simulation();
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local.AddRemoteSimulation("OTHER", remote);
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_ = local.ExecuteNonQuery("exec sp_addlinkedserver 'OTHER'");
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AreEqual(2, local.ExecuteScalar("select count(*) from sys.servers"));
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_ = local.ExecuteNonQuery("exec sp_dropserver 'OTHER'");
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AreEqual(1, local.ExecuteScalar("select count(*) from sys.servers"));
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}
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}

‎SqlServerSimulator.Tests/QualityTests.cs‎

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".ctor",
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nameof(Simulation.CreateDbConnection),
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nameof(Simulation.ImportBacpac),
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nameof(Simulation.AddRemoteSimulation),
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];
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Assert.HasCount(allowedMemberNames.Count, memberNames);

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