refactor(backups): MostRecentFullBackupLsn can return null (#106)

* refactor(backups): MostRecentFullBackupLsn can return null

Author: AdityaNPL

src/AgDatabase.cs

@@ -138,16 +138,14 @@ public List<BackupMetadata> RecentBackups()
       var fullBackupLsnBag = new ConcurrentBag<decimal>();
       _listener.ForEachAgInstance(s => 
       {
-        try
-        {
-          fullBackupLsnBag.Add(s.Database(Name).MostRecentFullBackupLsn());
-        }
-        catch { }
+        var lsn = s.Database(Name).MostRecentFullBackupLsn();
+        if (lsn != null)
+          fullBackupLsnBag.Add(lsn.Value);
       });
 
       // find all backups in that chain
       if (fullBackupLsnBag.IsEmpty)
-        throw new Exception($"Could not find any full backups for DB '{Name}'"); 
+        throw new Exception($"Could not find any full backups for DB '{Name}'");
 
       var databaseBackupLsn = fullBackupLsnBag.Max();
       var bag = new ConcurrentBag<BackupMetadata>();

src/SmoFacade/Database.cs

@@ -150,7 +150,7 @@ public List<BackupMetadata> MostRecentBackupChain()
       return backups;
     }
 
-    public decimal MostRecentFullBackupLsn()
+    public decimal? MostRecentFullBackupLsn()
     {
       var query = "SELECT MAX(checkpoint_lsn) as most_recent_full_backup_checkpoint_lsn " +
                   "FROM msdb.dbo.backupset " +
@@ -166,13 +166,12 @@ public decimal MostRecentFullBackupLsn()
       cmd.Parameters.Add(dbName);
 
       using var reader = cmd.ExecuteReader();
-      if (!reader.Read())
-        throw new Exception("MostRecentFullBackup SQL found no results");
+      if(!reader.Read())
+        return null;
 
       var lsnValue = reader["most_recent_full_backup_checkpoint_lsn"];
-
       if (lsnValue == DBNull.Value)
-        throw new Exception("MostRecentFullBackup SQL found no results");
+        return null;
 
       return (decimal)lsnValue;
     }
@@ -181,13 +180,13 @@ public List<BackupMetadata> BackupChainFromLsn(decimal checkpointLsn)
     {
       var backups = new List<BackupMetadata>();
 
-      var query = "SELECT s.database_name, m.physical_device_name, s.backup_start_date, s.first_lsn, s.last_lsn," +
+      var query = "SELECT s.database_name, m.physical_device_name, s.backup_start_date, s.first_lsn, s.last_lsn, " +
                   "s.database_backup_lsn, s.checkpoint_lsn, s.[type] AS backup_type, s.server_name, s.recovery_model " +
                   "FROM msdb.dbo.backupset s " +
                   "INNER JOIN msdb.dbo.backupmediafamily m ON s.media_set_id = m.media_set_id " +
                   "WHERE s.database_name = @dbName " +
                   "AND is_copy_only = 0 " +
-                  "AND (s.database_backup_lsn = @lsn OR s.checkpoint_lsn = @lsn)" +
+                  "AND (s.database_backup_lsn = @lsn OR s.checkpoint_lsn = @lsn) " +
                   "ORDER BY s.backup_start_date DESC, backup_finish_date";
 
       using var cmd = _server.SqlConnection.CreateCommand();
@@ -300,4 +299,4 @@ private void ThrowIfUnreadyToDrop()
       });
     }
   }
-}
+}