Fix relational mapping hints and add DbType

src/EFCore.Relational/Storage/RelationalTypeMapping.cs

@@ -137,7 +137,7 @@ public RelationalTypeMappingParameters WithTypeMappingInfo(in RelationalTypeMapp
                 CoreParameters,
                 mappingInfo.StoreTypeName ?? StoreType,
                 StoreTypePostfix,
-                DbType,
+                mappingInfo.DbType ?? DbType,
                 mappingInfo.IsUnicode ?? Unicode,
                 mappingInfo.Size ?? Size,
                 mappingInfo.IsFixedLength ?? FixedLength,

src/EFCore.Relational/Storage/RelationalTypeMappingInfo.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Data;
+
 namespace Microsoft.EntityFrameworkCore.Storage;
 
 /// <summary>
@@ -33,7 +35,7 @@ public RelationalTypeMappingInfo(IProperty property)
     /// <param name="fallbackUnicode">
     ///     Specifies Unicode or ANSI for the mapping or <see langword="null" /> for default.
     /// </param>
-    /// <param name="fixedLength">Specifies a fixed length mapping, or <see langword="null" /> for default.</param>
+    /// <param name="fallbackFixedLength">Specifies a fixed length mapping, or <see langword="null" /> for default.</param>
     /// <param name="fallbackSize">
     ///     Specifies a size for the mapping, in case one isn't found at the core level, or <see langword="null" /> for default.
     /// </param>
@@ -48,17 +50,43 @@ public RelationalTypeMappingInfo(
         string? storeTypeName = null,
         string? storeTypeNameBase = null,
         bool? fallbackUnicode = null,
-        bool? fixedLength = null,
+        bool? fallbackFixedLength = null,
         int? fallbackSize = null,
         int? fallbackPrecision = null,
         int? fallbackScale = null)
     {
         _coreTypeMappingInfo = new TypeMappingInfo(principals, fallbackUnicode, fallbackSize, fallbackPrecision, fallbackScale);
 
-        IsFixedLength = fixedLength;
+        ValueConverter? customConverter = null;
+        for (var i = 0; i < principals.Count; i++)
+        {
+            var principal = principals[i];
+            if (customConverter == null)
+            {
+                var converter = principal.GetValueConverter();
+                if (converter != null)
+                {
+                    customConverter = converter;
+                }
+            }
+
+            if (fallbackFixedLength == null)
+            {
+                var fixedLength = principal.IsFixedLength();
+                if (fixedLength != null)
+                {
+                    fallbackFixedLength = fixedLength;
+                }
+            }
+        }
+
+        var mappingHints = customConverter?.MappingHints;
+
+        IsFixedLength = fallbackFixedLength ?? (mappingHints as RelationalConverterMappingHints)?.IsFixedLength;
+        DbType = (mappingHints as RelationalConverterMappingHints)?.DbType;
         StoreTypeName = storeTypeName;
         StoreTypeNameBase = storeTypeNameBase;
-    }
+     }
 
     /// <summary>
     ///     Creates a new instance of <see cref="RelationalTypeMappingInfo" />.
@@ -132,6 +160,7 @@ public RelationalTypeMappingInfo(
         StoreTypeName = source.StoreTypeName;
         StoreTypeNameBase = source.StoreTypeNameBase;
         IsFixedLength = source.IsFixedLength ?? (mappingHints as RelationalConverterMappingHints)?.IsFixedLength;
+        DbType = source.DbType ?? (mappingHints as RelationalConverterMappingHints)?.DbType;
     }
 
     /// <summary>
@@ -208,6 +237,11 @@ public int? Scale
     /// </summary>
     public bool? IsFixedLength { get; init; }
 
+    /// <summary>
+    ///     The <see cref="DbType"/> of the mapping.
+    /// </summary>
+    public DbType? DbType { get; init; }
+
     /// <summary>
     ///     Indicates whether or not the mapping is part of a key or index.
     /// </summary>

src/EFCore.Relational/Storage/ValueConversion/RelationalConverterMappingHints.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Data;
+
 namespace Microsoft.EntityFrameworkCore.Storage.ValueConversion;
 
 /// <summary>
@@ -21,24 +23,45 @@ public class RelationalConverterMappingHints : ConverterMappingHints
     /// <param name="unicode">Whether or not the mapped data type should support Unicode.</param>
     /// <param name="fixedLength">Whether or not the mapped data type is fixed length.</param>
     /// <param name="valueGeneratorFactory">An optional factory for creating a specific <see cref="ValueGenerator" />.</param>
+    /// <param name="dbType">The suggested <see cref="DbType"/>.</param>
     public RelationalConverterMappingHints(
         int? size = null,
         int? precision = null,
         int? scale = null,
         bool? unicode = null,
         bool? fixedLength = null,
-        Func<IProperty, IEntityType, ValueGenerator>? valueGeneratorFactory = null)
+        Func<IProperty, IEntityType, ValueGenerator>? valueGeneratorFactory = null,
+        DbType? dbType = null)
         : base(size, precision, scale, unicode, valueGeneratorFactory)
     {
         IsFixedLength = fixedLength;
+        DbType = dbType;
     }
 
     /// <summary>
-    ///     Adds hints from the given object to this one. Hints that are already specified are
-    ///     not overridden.
+    ///     Creates a new <see cref="ConverterMappingHints" /> instance. Any hint contained in the instance
+    ///     can be <see langword="null" /> to indicate it has not been specified.
     /// </summary>
-    /// <param name="hints">The hints to add.</param>
-    /// <returns>The combined hints.</returns>
+    /// <param name="size">The suggested size of the mapped data type.</param>
+    /// <param name="precision">The suggested precision of the mapped data type.</param>
+    /// <param name="scale">The suggested scale of the mapped data type.</param>
+    /// <param name="unicode">Whether or not the mapped data type should support Unicode.</param>
+    /// <param name="fixedLength">Whether or not the mapped data type is fixed length.</param>
+    /// <param name="valueGeneratorFactory">An optional factory for creating a specific <see cref="ValueGenerator" />.</param>
+    [Obsolete("Use the overload with more parameters.")]
+    public RelationalConverterMappingHints(
+        int? size,
+        int? precision,
+        int? scale,
+        bool? unicode,
+        bool? fixedLength,
+        Func<IProperty, IEntityType, ValueGenerator>? valueGeneratorFactory)
+        : base(size, precision, scale, unicode, valueGeneratorFactory)
+    {
+        IsFixedLength = fixedLength;
+    }
+
+    /// <inheritdoc />
     public override ConverterMappingHints With(ConverterMappingHints? hints)
         => hints == null
             ? this
@@ -48,10 +71,29 @@ public override ConverterMappingHints With(ConverterMappingHints? hints)
                 hints.Scale ?? Scale,
                 hints.IsUnicode ?? IsUnicode,
                 (hints as RelationalConverterMappingHints)?.IsFixedLength ?? IsFixedLength,
-                hints.ValueGeneratorFactory ?? ValueGeneratorFactory);
+                hints.ValueGeneratorFactory ?? ValueGeneratorFactory,
+                (hints as RelationalConverterMappingHints)?.DbType ?? DbType);
+
+    /// <inheritdoc />
+    public override ConverterMappingHints Override(ConverterMappingHints? hints)
+        => hints == null
+            ? this
+            : new RelationalConverterMappingHints(
+                Size ?? hints.Size,
+                Precision ?? hints.Precision,
+                Scale ?? hints.Scale,
+                IsUnicode ?? hints.IsUnicode,
+                IsFixedLength ?? (hints as RelationalConverterMappingHints)?.IsFixedLength,
+                ValueGeneratorFactory ?? hints.ValueGeneratorFactory,
+                DbType ?? (hints as RelationalConverterMappingHints)?.DbType);
 
     /// <summary>
     ///     Whether or not the mapped data type is fixed length.
     /// </summary>
     public virtual bool? IsFixedLength { get; }
+
+    /// <summary>
+    ///     The suggested <see cref="DbType"/>
+    /// </summary>
+    public virtual DbType? DbType { get; }
 }

src/EFCore/Storage/ValueConversion/ConverterMappingHints.cs

@@ -38,8 +38,7 @@ public ConverterMappingHints(
     }
 
     /// <summary>
-    ///     Adds hints from the given object to this one. Hints that are already specified are
-    ///     not overridden.
+    ///     Adds hints from the given object to this one. Hints that are already specified are not overridden.
     /// </summary>
     /// <remarks>
     ///     See <see href="https://aka.ms/efcore-docs-value-converters">EF Core value converters</see> for more information and examples.
@@ -49,12 +48,34 @@ public ConverterMappingHints(
     public virtual ConverterMappingHints With(ConverterMappingHints? hints)
         => hints == null
             ? this
-            : new ConverterMappingHints(
-                hints.Size ?? Size,
-                hints.Precision ?? Precision,
-                hints.Scale ?? Scale,
-                hints.IsUnicode ?? IsUnicode,
-                hints.ValueGeneratorFactory ?? ValueGeneratorFactory);
+            : hints.GetType().IsAssignableFrom(GetType())
+                ? new ConverterMappingHints(
+                    hints.Size ?? Size,
+                    hints.Precision ?? Precision,
+                    hints.Scale ?? Scale,
+                    hints.IsUnicode ?? IsUnicode,
+                    hints.ValueGeneratorFactory ?? ValueGeneratorFactory)
+                : hints.Override(this);
+
+    /// <summary>
+    ///     Adds hints from the given object to this one. Hints that are already specified are overridden.
+    /// </summary>
+    /// <remarks>
+    ///     See <see href="https://aka.ms/efcore-docs-value-converters">EF Core value converters</see> for more information and examples.
+    /// </remarks>
+    /// <param name="hints">The hints to add.</param>
+    /// <returns>The combined hints.</returns>
+    public virtual ConverterMappingHints Override(ConverterMappingHints? hints)
+        => hints == null
+            ? this
+            : GetType().IsAssignableFrom(hints.GetType())
+                ? new ConverterMappingHints(
+                    Size ?? hints.Size,
+                    Precision ?? hints.Precision,
+                    Scale ?? hints.Scale,
+                    IsUnicode ?? hints.IsUnicode,
+                    ValueGeneratorFactory ?? hints.ValueGeneratorFactory)
+                : hints.With(this);
 
     /// <summary>
     ///     The suggested size of the mapped data type.

test/EFCore.SqlServer.FunctionalTests/ValueConvertersEndToEndSqlServerTest.cs

@@ -3,6 +3,8 @@
 
 #nullable enable
 
+using System.Data;
+
 namespace Microsoft.EntityFrameworkCore;
 
 public class ValueConvertersEndToEndSqlServerTest
@@ -194,6 +196,78 @@ public WrappedStringToStringConverter()
         }
     }
 
+    [ConditionalFact]
+    public virtual void Fixed_length_hints_are_respected()
+    {
+        Fixture.TestSqlLoggerFactory.Clear();
+
+        using var context = CreateContext();
+
+        var guid = new Guid("d854227f-7076-48c3-997c-4e72c1c713b9");
+
+        var mapping = context.Set<SqlServerConvertingEntity>()
+            .EntityType
+            .FindProperty(nameof(SqlServerConvertingEntity.GuidToFixedLengthString))!
+            .FindRelationalTypeMapping()!;
+
+        Assert.Equal("nchar(40)", mapping.StoreType);
+        Assert.Equal(40, mapping.Size);
+
+        Assert.Empty(context.Set<SqlServerConvertingEntity>().Where(e => e.GuidToFixedLengthString != guid));
+
+        Assert.Equal(
+"""
+@__guid_0='d854227f-7076-48c3-997c-4e72c1c713b9' (Nullable = false) (Size = 40)
+
+SELECT [s].[Id], [s].[GuidToDbTypeString], [s].[GuidToFixedLengthString]
+FROM [SqlServerConvertingEntity] AS [s]
+WHERE [s].[GuidToFixedLengthString] <> @__guid_0
+""",
+            Fixture.TestSqlLoggerFactory.SqlStatements[0],
+            ignoreLineEndingDifferences: true);
+
+        var parameter = Fixture.TestSqlLoggerFactory.Parameters.Single();
+    }
+
+    [ConditionalFact]
+    public virtual void DbType_hints_are_respected()
+    {
+        Fixture.TestSqlLoggerFactory.Clear();
+
+        using var context = CreateContext();
+
+        var mapping = context.Set<SqlServerConvertingEntity>()
+            .EntityType
+            .FindProperty(nameof(SqlServerConvertingEntity.GuidToDbTypeString))!
+            .FindRelationalTypeMapping()!;
+
+        Assert.Equal(DbType.AnsiStringFixedLength, mapping.DbType!);
+        Assert.Equal(40, mapping.Size);
+
+        var guid = new Guid("d854227f-7076-48c3-997c-4e72c1c713b9");
+
+        Assert.Empty(context.Set<SqlServerConvertingEntity>().Where(e => e.GuidToDbTypeString != guid));
+
+        Assert.Equal(
+"""
+@__guid_0='d854227f-7076-48c3-997c-4e72c1c713b9' (Nullable = false) (Size = 40) (DbType = AnsiStringFixedLength)
+
+SELECT [s].[Id], [s].[GuidToDbTypeString], [s].[GuidToFixedLengthString]
+FROM [SqlServerConvertingEntity] AS [s]
+WHERE [s].[GuidToDbTypeString] <> @__guid_0
+""",
+            Fixture.TestSqlLoggerFactory.SqlStatements[0],
+            ignoreLineEndingDifferences: true);
+    }
+
+    protected class SqlServerConvertingEntity
+    {
+        public Guid Id { get; set; }
+
+        public Guid GuidToFixedLengthString { get; set; }
+        public Guid GuidToDbTypeString { get; set; }
+    }
+
     public class ValueConvertersEndToEndSqlServerFixture : ValueConvertersEndToEndFixtureBase
     {
         protected override void ConfigureConventions(ModelConfigurationBuilder configurationBuilder)
@@ -221,6 +295,20 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                     b.Property(e => e.NullableEnumerableOfInt).HasDefaultValue(Enumerable.Empty<int>());
                     b.Property(e => e.EnumerableOfInt).HasDefaultValue(Enumerable.Empty<int>());
                 });
+
+            modelBuilder.Entity<SqlServerConvertingEntity>(
+                b =>
+                {
+                    b.Property(e => e.GuidToFixedLengthString).HasConversion(
+                        new GuidToStringConverter(
+                            new RelationalConverterMappingHints(
+                                size: 40, fixedLength: true)));
+
+                    b.Property(e => e.GuidToDbTypeString).HasConversion(
+                        new GuidToStringConverter(
+                            new RelationalConverterMappingHints(
+                                size: 40, unicode: false, dbType: DbType.AnsiStringFixedLength)));
+                });
         }
     }
 }