Fix mapping of MinLength/MaxLength/Length attribute mapping in nullable string properties. (#6812)

Author: eiriktsarpalis

src/Libraries/Microsoft.Extensions.AI.Abstractions/Utilities/AIJsonUtilities.Schema.Create.cs

@@ -427,7 +427,7 @@ void ApplyDataAnnotations(ref JsonNode schema, AIJsonSchemaCreateContext ctx)
                 if (ResolveAttribute<MinLengthAttribute>() is { } minLengthAttribute)
                 {
                     JsonObject obj = ConvertSchemaToObject(ref schema);
-                    if (obj[TypePropertyName] is JsonNode typeNode && typeNode.GetValueKind() is JsonValueKind.String && typeNode.GetValue<string>() is "string")
+                    if (TryGetSchemaType(obj, out string? schemaType, out _) && schemaType is "string")
                     {
                         obj[MinLengthStringPropertyName] ??= minLengthAttribute.Length;
                     }
@@ -440,7 +440,7 @@ void ApplyDataAnnotations(ref JsonNode schema, AIJsonSchemaCreateContext ctx)
                 if (ResolveAttribute<MaxLengthAttribute>() is { } maxLengthAttribute)
                 {
                     JsonObject obj = ConvertSchemaToObject(ref schema);
-                    if (obj[TypePropertyName] is JsonNode typeNode && typeNode.GetValueKind() is JsonValueKind.String && typeNode.GetValue<string>() is "string")
+                    if (TryGetSchemaType(obj, out string? schemaType, out _) && schemaType is "string")
                     {
                         obj[MaxLengthStringPropertyName] ??= maxLengthAttribute.Length;
                     }
@@ -530,7 +530,7 @@ void ApplyDataAnnotations(ref JsonNode schema, AIJsonSchemaCreateContext ctx)
                 {
                     JsonObject obj = ConvertSchemaToObject(ref schema);
 
-                    if (obj[TypePropertyName] is JsonNode typeNode && typeNode.GetValueKind() is JsonValueKind.String && typeNode.GetValue<string>() is "string")
+                    if (TryGetSchemaType(obj, out string? schemaType, out _) && schemaType is "string")
                     {
                         if (lengthAttribute.MinimumLength > 0)
                         {
@@ -629,6 +629,58 @@ static JsonArray CreateJsonArray(object?[] values, JsonSerializerOptions seriali
                     }
                 }
 #endif
+#if NET || NETFRAMEWORK
+                static bool TryGetSchemaType(JsonObject schema, [NotNullWhen(true)] out string? schemaType, out bool isNullable)
+                {
+                    schemaType = null;
+                    isNullable = false;
+
+                    if (!schema.TryGetPropertyValue(TypePropertyName, out JsonNode? typeNode))
+                    {
+                        return false;
+                    }
+
+                    switch (typeNode?.GetValueKind())
+                    {
+                        case JsonValueKind.String:
+                            schemaType = typeNode.GetValue<string>();
+                            return true;
+
+                        case JsonValueKind.Array:
+                            string? foundSchemaType = null;
+                            foreach (JsonNode? entry in (JsonArray)typeNode)
+                            {
+                                if (entry?.GetValueKind() is not JsonValueKind.String)
+                                {
+                                    return false;
+                                }
+
+                                string entryValue = entry.GetValue<string>();
+                                if (entryValue is "null")
+                                {
+                                    isNullable = true;
+                                    continue;
+                                }
+
+                                if (foundSchemaType is null)
+                                {
+                                    foundSchemaType = entryValue;
+                                }
+                                else if (foundSchemaType != entryValue)
+                                {
+                                    return false;
+                                }
+                            }
+
+                            schemaType = foundSchemaType;
+                            return schemaType is not null;
+
+                        default:
+                            return false;
+                    }
+                }
+#endif
+
                 TAttribute? ResolveAttribute<TAttribute>()
                     where TAttribute : Attribute
                 {

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Utilities/AIJsonUtilitiesTests.cs

@@ -670,22 +670,22 @@ public static void CreateJsonSchema_IncorporatesTypesAndAnnotations_Net()
                             "string",
                             "null"
                         ],
-                        "minItems": 5
+                        "minLength": 5
                     },
                     "MaxLengthProp": {
                         "type": [
                             "string",
                             "null"
                         ],
-                        "maxItems": 50
+                        "maxLength": 50
                     },
                     "LengthProp": {
                         "type": [
                             "string",
                             "null"
                         ],
-                        "minItems": 3,
-                        "maxItems": 10
+                        "minLength": 3,
+                        "maxLength": 10
                     },
                     "MinLengthArrayProp": {
                         "type": [
@@ -848,14 +848,14 @@ public static void CreateJsonSchema_IncorporatesTypesAndAnnotations_NetFx()
                             "string",
                             "null"
                         ],
-                        "minItems": 5
+                        "minLength": 5
                     },
                     "MaxLengthProp": {
                         "type": [
                             "string",
                             "null"
                         ],
-                        "maxItems": 50
+                        "maxLength": 50
                     },
                     "MinLengthArrayProp": {
                         "type": [
@@ -972,6 +972,33 @@ private sealed class CreateJsonSchema_IncorporatesTypesAndAnnotations_Type
 #endif
     }
 
+    [Fact]
+    public static void ClassWithNullableMaxLengthProperty_ReturnsExpectedSchema()
+    {
+        JsonElement expectedSchema = JsonDocument.Parse("""
+        {
+            "type": "object",
+            "properties": {
+                "Value": {
+                    "type": ["string", "null"],
+                    "maxLength": 24,
+                    "minLength": 10
+                }
+            }
+        }
+        """).RootElement;
+
+        JsonElement actualSchema = AIJsonUtilities.CreateJsonSchema(typeof(ClassWithNullableMaxLengthProperty), serializerOptions: JsonContext.Default.Options);
+        AssertDeepEquals(expectedSchema, actualSchema);
+    }
+
+    public class ClassWithNullableMaxLengthProperty
+    {
+        [MinLength(10)]
+        [MaxLength(24)]
+        public string? Value { get; set; }
+    }
+
     [Fact]
     public static void AddAIContentType_DerivedAIContent()
     {
@@ -1362,6 +1389,7 @@ private class DerivedAIContent : AIContent
     [JsonSerializable(typeof(MyPoco))]
     [JsonSerializable(typeof(MyEnumValue?))]
     [JsonSerializable(typeof(object[]))]
+    [JsonSerializable(typeof(ClassWithNullableMaxLengthProperty))]
     private partial class JsonContext : JsonSerializerContext;
 
     private static bool DeepEquals(JsonElement element1, JsonElement element2)