Refactor 'ObjectListFilter' to use 'System.Text.Json' coercion

Replaces custom value coercers with 'System.Text.Json'-based coercion in 'ObjectListFilter', supporting advanced scenarios like F# DUs and CLR enums via 'JsonSerializerOptions'. Updates 'ObjectListFilterLinqOptions' to accept 'JsonSerializerOptions'. Refactors 'TypeCoercion' module to use JSON serialization/deserialization for all type conversions. Updates filter application logic and expands the test suite with new files to cover a wide range of coercion scenarios. Updates documentation and usage examples accordingly.

Author: xperiandri

src/FSharp.Data.GraphQL.Server.Middleware/ObjectListFilter.fs

@@ -2,6 +2,7 @@ namespace FSharp.Data.GraphQL.Server.Middleware
 
 open System
 open System.Collections
+open System.Text.Json
 open FSharp.Data.GraphQL
 
 /// A filter definition for a field value.
@@ -46,25 +47,19 @@ type private CompareDiscriminatorExpression<'T, 'D> = Expression<Func<'T, 'D, bo
 type ObjectListFilterValidationException (message : string, [<Optional>] extensions : Dictionary<string, obj> | null) =
     inherit GQLMessageExceptionBase (ErrorKind.Validation, message, extensions)
 
-/// <summary>
-/// Function signature for custom value coercion logic. Takes a target CLR type and a JSON
-/// primitive value, returns the coerced value or <see langword="ValueNone"/> if coercion is not supported.
-/// </summary>
-type FilterValueCoercer = Type -> obj -> obj voption
-
 /// <summary>
 /// Optional configuration for LINQ translation including discriminator handling.
 /// </summary>
 type ObjectListFilterLinqOptions<'T, 'D>
     (
         [<Optional>] compareDiscriminator : CompareDiscriminatorExpression<'T, 'D> | null,
         [<Optional>] getDiscriminatorValue : (Type -> 'D) | null,
-        [<Optional>] customCoercers : FilterValueCoercer list | null
+        [<Optional>] jsonOptions : JsonSerializerOptions | null
     ) =
 
     member _.CompareDiscriminator = compareDiscriminator |> ValueOption.ofObj
     member _.GetDiscriminatorValue = getDiscriminatorValue |> ValueOption.ofObj
-    member _.CustomCoercers = customCoercers |> Option.ofObj |> Option.defaultValue []
+    member _.JsonOptions = jsonOptions |> ValueOption.ofObj
 
     static member None = ObjectListFilterLinqOptions<'T, 'D> (null, null, null)
 
@@ -82,10 +77,10 @@ type ObjectListFilterLinqOptions<'T, 'D>
         ObjectListFilterLinqOptions<'T, 'D> (null, getDiscriminatorValue, null)
     new (getDiscriminator : Expression<Func<'T, 'D>>, getDiscriminatorValue : Type -> 'D) =
         ObjectListFilterLinqOptions<'T, 'D> (ObjectListFilterLinqOptions.GetCompareDiscriminator getDiscriminator, getDiscriminatorValue, null)
-    new (customCoercers : FilterValueCoercer list) =
-        ObjectListFilterLinqOptions<'T, 'D> (null, null, customCoercers)
-    new (getDiscriminator : Expression<Func<'T, 'D>>, customCoercers : FilterValueCoercer list) =
-        ObjectListFilterLinqOptions<'T, 'D> (ObjectListFilterLinqOptions.GetCompareDiscriminator getDiscriminator, null, customCoercers)
-    new (compareDiscriminator : CompareDiscriminatorExpression<'T, 'D>, customCoercers : FilterValueCoercer list) =
-        ObjectListFilterLinqOptions<'T, 'D> (compareDiscriminator, null, customCoercers)
+    new (jsonOptions : JsonSerializerOptions) =
+        ObjectListFilterLinqOptions<'T, 'D> (null, null, jsonOptions)
+    new (getDiscriminator : Expression<Func<'T, 'D>>, jsonOptions : JsonSerializerOptions) =
+        ObjectListFilterLinqOptions<'T, 'D> (ObjectListFilterLinqOptions.GetCompareDiscriminator getDiscriminator, null, jsonOptions)
+    new (compareDiscriminator : CompareDiscriminatorExpression<'T, 'D>, jsonOptions : JsonSerializerOptions) =
+        ObjectListFilterLinqOptions<'T, 'D> (compareDiscriminator, null, jsonOptions)
 

src/FSharp.Data.GraphQL.Server.Middleware/ObjectListFilterModule.fs

@@ -196,8 +196,10 @@ module ObjectListFilter =
                 | NonEnumerableCast _ ->
                     Expression.NotEqual (Expression.Convert (``member``, objectType), Expression.Convert ((Expression.Constant f.Value), objectType))
                 | Enumerable ->
-                    let ``const`` = Expression.Constant (Values.normalizeOptional ``member``.Type f.Value)
-                    Expression.Not (Expression.Call (``const``, equalsMethod, ``member``))
+                    let normalized = Values.normalizeOptional ``member``.Type f.Value
+                    let ``const`` = Expression.Constant (normalized)
+                    let boxedArg = Expression.Convert (``member``, objectType)
+                    Expression.Not (Expression.Call (``const``, equalsMethod, boxedArg))
         | Not f -> f |> build |> Expression.Not :> Expression
         | And (f1, f2) -> Expression.AndAlso (build f1, build f2)
         | Or (f1, f2) -> Expression.OrElse (build f1, build f2)
@@ -215,8 +217,10 @@ module ObjectListFilter =
                 | NonEnumerableCast _ ->
                     Expression.Equal (Expression.Convert (``member``, objectType), Expression.Convert ((Expression.Constant f.Value), objectType))
                 | Enumerable ->
-                    let ``const`` = Expression.Constant (Values.normalizeOptional ``member``.Type f.Value)
-                    Expression.Call (``const``, equalsMethod, ``member``)
+                    let normalized = Values.normalizeOptional ``member``.Type f.Value
+                    let ``const`` = Expression.Constant (normalized)
+                    let boxedArg = Expression.Convert (``member``, objectType)
+                    Expression.Call (``const``, equalsMethod, boxedArg)
         | GreaterThan f ->
             let ``member`` = Expression.PropertyOrField (param, f.FieldName)
             match f.Value with
@@ -362,59 +366,41 @@ module ObjectListFilterExtensions =
         /// <summary>
         /// Applies the filter to a queryable with automatic type coercion of JSON primitives to CLR types.
         /// Supports <see cref="Guid"/>, <see cref="DateTime"/>, <see cref="DateTimeOffset"/>, <see cref="DateOnly"/>, and F# discriminated unions.
-        /// Pass custom coercers via <c>ObjectListFilterLinqOptions</c> constructor.
+        /// Pass <see cref="JsonSerializerOptions"/> via <c>ObjectListFilterLinqOptions</c> constructor for custom serialization.
         /// </summary>
         /// <example>
         /// <code>
         /// // Basic usage - automatic coercion of string to Guid
         /// let filter = "id" === "550e8400-e29b-41d4-a716-446655440000"
         /// let users = filter.ApplyTo query
         ///
-        /// // With custom coercer for NodaTime.Instant
-        /// let nodaCoercer : FilterValueCoercer = fun targetType value ->
-        ///     if targetType = typeof&lt;NodaTime.Instant&gt; then
-        ///         match value with
-        ///         | :? string as s ->
-        ///             let parsed = NodaTime.Text.InstantPattern.ExtendedIso.Parse s
-        ///             if parsed.Success then ValueSome (box parsed.Value)
-        ///             else ValueNone
-        ///         | _ -> ValueNone
-        ///     else ValueNone
-        ///
-        /// let options = ObjectListFilterLinqOptions([nodaCoercer])
+        /// // With custom JsonSerializerOptions
+        /// let opts = JsonSerializerOptions(PropertyNameCaseInsensitive = true)
+        /// let options = ObjectListFilterLinqOptions(opts)
         /// let events = filter.ApplyTo(query, options)
         /// </code>
         /// </example>
         member inline filter.ApplyTo<'T, 'D> (query : IQueryable<'T>, [<Optional>] options : ObjectListFilterLinqOptions<'T, 'D> | null) =
             let options = options |> ValueOption.ofObj |> ValueOption.defaultValue ObjectListFilterLinqOptions<'T, 'D>.None
-            let filter = TypeCoercion.coerceFilter options.CustomCoercers typeof<'T> filter
+            let filter = TypeCoercion.coerceFilter options.JsonOptions typeof<'T> filter
             apply options filter query
 
     type IQueryable<'T> with
 
         /// <summary>
         /// Applies the filter with automatic type coercion of JSON primitives to CLR types. Supports <see cref="Guid"/>, <see cref="DateTime"/>,
-        /// <see cref="DateTimeOffset"/>, <see cref="DateOnly"/>, and F# discriminated unions. Pass custom coercers via <c>
-        /// ObjectListFilterLinqOptions</c> constructor.
+        /// <see cref="DateTimeOffset"/>, <see cref="DateOnly"/>, and F# discriminated unions. Pass <see cref="JsonSerializerOptions"/> via <c>
+        /// ObjectListFilterLinqOptions</c> constructor for custom serialization.
         /// </summary>
         /// <example>
         /// <code>
         /// // Basic usage - automatic coercion of string to Guid
         /// let filter = "id" === "550e8400-e29b-41d4-a716-446655440000"
         /// let users = query.Apply filter
         ///
-        /// // With custom coercer for NodaTime.Instant
-        /// let nodaCoercer : FilterValueCoercer = fun targetType value ->
-        ///     if targetType = typeof&lt;NodaTime.Instant&gt; then
-        ///         match value with
-        ///         | :? string as s ->
-        ///             let parsed = NodaTime.Text.InstantPattern.ExtendedIso.Parse s
-        ///             if parsed.Success then ValueSome (box parsed.Value)
-        ///             else ValueNone
-        ///         | _ -> ValueNone
-        ///     else ValueNone
-        ///
-        /// let options = ObjectListFilterLinqOptions([nodaCoercer])
+        /// // With custom JsonSerializerOptions
+        /// let opts = JsonSerializerOptions(PropertyNameCaseInsensitive = true)
+        /// let options = ObjectListFilterLinqOptions(opts)
         /// let events = query.Apply(filter, options)
         /// </code>
         /// </example>