Restore WithProjection(LambdaExpression) and add nav isNull

docs/mdsource/query-usage.source.md

@@ -211,7 +211,7 @@ To negate an expression, including a group, wrap it in `not`:
 
 #### Nested Properties
 
-A reference navigation, owned type or complex property is a nested where object. No null checking of nested values is done.
+A reference navigation, owned type or complex property is a nested where object. No null checking of nested values is done; to test the navigation itself see [Null](#null).
 
 ```graphql
 {
@@ -263,6 +263,23 @@ Null is compared with a null value:
 
 An empty where, `{}`, applies no filter.
 
+A reference navigation is tested with `isNull`, since a nested where can only constrain the members
+of the navigation, not the navigation itself:
+
+```graphql
+{
+  entities
+  (where: {address: {isNull: true}})
+  {
+    property
+  }
+}
+```
+
+`isNull: false` requires the navigation to be present. A collection navigation uses `none: {}` and
+`any: {}` instead. `isNull` has no meaning at the root of a where, since there is no navigation it
+was reached through.
+
 
 #### Variables
 

docs/mdsource/upgradeGuide35.source.md

@@ -16,7 +16,9 @@ From [#1377](https://github.com/SimonCropp/GraphQL.EntityFramework/pull/1377). T
  * The extension methods `Resolve`, `ResolveAsync`, `ResolveList` and `ResolveListAsync` take the `IEfGraphQLService<TDbContext>` as their first argument. All type arguments are inferred, and the service is used directly at execution time instead of being located through `RequestServices`.
  * `FieldBuilderResolveAnalyzer` previously never matched the extension methods, so GQLEF003 could not fire. It now resolves the receiver type for extension methods and identifies projection based calls by their `projection` parameter.
 
-The old extension methods and the `LambdaExpression` overload of `WithProjection` are removed rather than kept as overloads.
+The old extension methods are removed rather than kept as overloads. The `LambdaExpression` overload
+of `WithProjection` was removed in 35.0.0 and restored in 35.1.0, for a projection built by
+reflection or by `Expression.Lambda`, where the caller does not have the source and projection types.
 
 
 ### WithProjection
@@ -111,6 +113,7 @@ input PersonWhere {
   and: [PersonWhere!]
   or: [PersonWhere!]
   not: PersonWhere
+  isNull: Boolean
   id: GuidComparison
   name: StringComparison
   age: Int32Comparison
@@ -538,6 +541,35 @@ After, pass null:
 
 An empty where, `{}`, applies no filter. The old empty list, `[]`, matched nothing.
 
+A path that named a reference navigation rather than one of its properties tested the navigation
+itself. The nested where has no comparison of its own, so use `isNull` (added in 35.1.0).
+
+Before:
+
+```graphql
+{
+  entities (where: {path: "Address", comparison: equal})
+  {
+    property
+  }
+}
+```
+
+After:
+
+```graphql
+{
+  entities (where: {address: {isNull: true}})
+  {
+    property
+  }
+}
+```
+
+`isNull: false` requires the navigation to be present, as `comparison: notEqual` did. A collection
+navigation uses `none: {}` and `any: {}` instead, and `isNull` is rejected at the root of a where,
+where there is no navigation it was reached through.
+
 
 ### Variables
 

docs/query-usage.md

@@ -218,7 +218,7 @@ To negate an expression, including a group, wrap it in `not`:
 
 #### Nested Properties
 
-A reference navigation, owned type or complex property is a nested where object. No null checking of nested values is done.
+A reference navigation, owned type or complex property is a nested where object. No null checking of nested values is done; to test the navigation itself see [Null](#null).
 
 ```graphql
 {
@@ -270,6 +270,23 @@ Null is compared with a null value:
 
 An empty where, `{}`, applies no filter.
 
+A reference navigation is tested with `isNull`, since a nested where can only constrain the members
+of the navigation, not the navigation itself:
+
+```graphql
+{
+  entities
+  (where: {address: {isNull: true}})
+  {
+    property
+  }
+}
+```
+
+`isNull: false` requires the navigation to be present. A collection navigation uses `none: {}` and
+`any: {}` instead. `isNull` has no meaning at the root of a where, since there is no navigation it
+was reached through.
+
 
 #### Variables
 

docs/upgradeGuide35.md

@@ -23,7 +23,9 @@ From [#1377](https://github.com/SimonCropp/GraphQL.EntityFramework/pull/1377). T
  * The extension methods `Resolve`, `ResolveAsync`, `ResolveList` and `ResolveListAsync` take the `IEfGraphQLService<TDbContext>` as their first argument. All type arguments are inferred, and the service is used directly at execution time instead of being located through `RequestServices`.
  * `FieldBuilderResolveAnalyzer` previously never matched the extension methods, so GQLEF003 could not fire. It now resolves the receiver type for extension methods and identifies projection based calls by their `projection` parameter.
 
-The old extension methods and the `LambdaExpression` overload of `WithProjection` are removed rather than kept as overloads.
+The old extension methods are removed rather than kept as overloads. The `LambdaExpression` overload
+of `WithProjection` was removed in 35.0.0 and restored in 35.1.0, for a projection built by
+reflection or by `Expression.Lambda`, where the caller does not have the source and projection types.
 
 
 ### WithProjection
@@ -118,6 +120,7 @@ input PersonWhere {
   and: [PersonWhere!]
   or: [PersonWhere!]
   not: PersonWhere
+  isNull: Boolean
   id: GuidComparison
   name: StringComparison
   age: Int32Comparison
@@ -545,6 +548,35 @@ After, pass null:
 
 An empty where, `{}`, applies no filter. The old empty list, `[]`, matched nothing.
 
+A path that named a reference navigation rather than one of its properties tested the navigation
+itself. The nested where has no comparison of its own, so use `isNull` (added in 35.1.0).
+
+Before:
+
+```graphql
+{
+  entities (where: {path: "Address", comparison: equal})
+  {
+    property
+  }
+}
+```
+
+After:
+
+```graphql
+{
+  entities (where: {address: {isNull: true}})
+  {
+    property
+  }
+}
+```
+
+`isNull: false` requires the navigation to be present, as `comparison: notEqual` did. A collection
+navigation uses `none: {}` and `any: {}` instead, and `isNull` is rejected at the root of a where,
+where there is no navigation it was reached through.
+
 
 ### Variables
 

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;NU5104;CS1573;CS9107;NU1608;NU1109;SC023</NoWarn>
-    <Version>35.0.0</Version>
+    <Version>35.1.0</Version>
     <LangVersion>preview</LangVersion>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <PackageTags>EntityFrameworkCore, EntityFramework, GraphQL</PackageTags>

src/GraphQL.EntityFramework/GraphApi/FieldBuilderExtensions.cs

@@ -360,7 +360,26 @@ public static FieldBuilder<TSource, TReturn> WithProjection<TSource, TReturn, TP
         return builder;
     }
 
-    static void ValidateProjection<TSource, TProjection>(Expression<Func<TSource, TProjection>> projection)
+    /// <summary>
+    /// Sets projection metadata on a field from a projection whose type is only known at runtime.
+    /// Prefer the <see cref="Expression{TDelegate}"/> overload, which infers its type arguments and
+    /// is checked at compile time. This one is for a projection built by reflection or by
+    /// <see cref="Expression.Lambda(Expression,ParameterExpression[])"/>, where the source and
+    /// projection types are not available to the caller.
+    /// </summary>
+    /// <param name="builder">The field builder</param>
+    /// <param name="projection">Expression describing the required entity data. Its parameter must be <typeparamref name="TSource"/> or a type it derives from.</param>
+    /// <returns>The field builder for chaining</returns>
+    public static FieldBuilder<TSource, TReturn> WithProjection<TSource, TReturn>(
+        this FieldBuilder<TSource, TReturn> builder,
+        LambdaExpression projection)
+    {
+        ValidateProjection(projection);
+        IncludeAppender.SetProjectionMetadata(builder.FieldType, projection);
+        return builder;
+    }
+
+    static void ValidateProjection(LambdaExpression projection)
     {
         // Detect identity projection: _ => _
         if (projection.Body is ParameterExpression parameter &&

src/GraphQL.EntityFramework/Where/ExpressionBuilder.cs

@@ -91,6 +91,13 @@ public static Expression<Func<T, bool>> BuildPredicate(WhereExpression where) =>
 
     static Expression MakePredicateBody(string path, Comparison comparison, object?[]? values, bool negate)
     {
+        if (path.Length == 0)
+        {
+            // isNull tests the navigation a nested where was reached through, so there is nothing
+            // to test at the root of a where.
+            throw new($"isNull is only valid on a navigation. It was used at the root of the where for {typeof(T).Name}.");
+        }
+
         try
         {
             Expression expressionBody;

src/GraphQL.EntityFramework/Where/Graphs/WhereGraph.cs

@@ -3,8 +3,10 @@ namespace GraphQL.EntityFramework;
 /// <summary>
 /// The where input type for <typeparamref name="TEntity"/>. One field per mapped property,
 /// typed by its comparisons, one per navigation, and <c>and</c>, <c>or</c> and <c>not</c> to
-/// compose them. Sibling fields are and'ed. The parsed value is a <see cref="WhereExpression"/>
-/// tree, so the predicate builder is unchanged.
+/// compose them. Sibling fields are and'ed. <c>isNull</c> tests the navigation this where was
+/// reached through, which is the one thing a nested where cannot say with its own fields; it has
+/// no meaning at the root. The parsed value is a <see cref="WhereExpression"/> tree, so the
+/// predicate builder is unchanged.
 /// </summary>
 public class WhereGraph<TEntity> :
     InputObjectGraphType,
@@ -55,6 +57,11 @@ public WhereGraph(IEnumerable<IEfGraphQLService> services)
             Name = "not",
             Type = self
         });
+        AddField(new()
+        {
+            Name = "isNull",
+            Type = typeof(BooleanGraphType)
+        });
 
         foreach (var member in EntityShape.Members(type, services))
         {
@@ -104,6 +111,14 @@ public override object ParseDictionary(IDictionary<string, object?> value)
                         expressions.Add(negated);
                     }
 
+                    continue;
+                case "isNull":
+                    // The navigation itself, rather than a member of it. Prefix turns the empty
+                    // path into the navigation's name.
+                    expressions.Add(new()
+                    {
+                        Comparison = (bool) raw ? Comparison.Equal : Comparison.NotEqual
+                    });
                     continue;
             }
 
@@ -219,6 +234,6 @@ static void Prefix(WhereExpression expression, string name)
             return;
         }
 
-        expression.Path = $"{name}.{expression.Path}";
+        expression.Path = expression.Path.Length == 0 ? name : $"{name}.{expression.Path}";
     }
 }

src/GraphQL.EntityFramework/Where/TypeConverter.cs

@@ -123,6 +123,13 @@ static bool ParseBoolean(string value) =>
 
         if (value is null)
         {
+            // Null is a meaningful comparison for a reference typed member: a navigation with no
+            // related row. Only a non nullable value type has nothing to compare against.
+            if (!type.IsValueType)
+            {
+                return null;
+            }
+
             throw new($"Null passed for non nullable type '{type.FullName}'.");
         }
 

src/SampleWeb.Tests/SchemaPrint.Print.verified.txt

@@ -69,6 +69,7 @@ input EmployeeWhere {
   and: [EmployeeWhere!]
   or: [EmployeeWhere!]
   not: EmployeeWhere
+  isNull: Boolean
   age: Int32Comparison
   company: CompanyWhere
   companyId: Int32Comparison
@@ -91,6 +92,7 @@ input CompanyWhere {
   and: [CompanyWhere!]
   or: [CompanyWhere!]
   not: CompanyWhere
+  isNull: Boolean
   content: StringComparison
   employees: EmployeeCollectionWhere
   id: Int32Comparison
@@ -122,6 +124,7 @@ input DeviceWhere {
   and: [DeviceWhere!]
   or: [DeviceWhere!]
   not: DeviceWhere
+  isNull: Boolean
   employees: EmployeeCollectionWhere
   id: Int32Comparison
   name: StringComparison