diff --git a/Extensions/FreeSql.Extensions.JsonMap/JsonMapCore.cs b/Extensions/FreeSql.Extensions.JsonMap/JsonMapCore.cs
index a0f6855d..24262eab 100644
--- a/Extensions/FreeSql.Extensions.JsonMap/JsonMapCore.cs
+++ b/Extensions/FreeSql.Extensions.JsonMap/JsonMapCore.cs
@@ -49,6 +49,7 @@ public static class FreeSqlJsonMapCoreExtensions
             if (isJsonMap)
             {
                 e.ModifyResult.MapType = typeof(string);
+                e.ModifyResult.StringLength = -2;
                 if (_dicTypes.TryAdd(e.Property.PropertyType, true))
                 {
                     FreeSql.Internal.Utils.GetDataReaderValueBlockExpressionObjectToStringIfThenElse.Add((LabelTarget returnTarget, Expression valueExp, Expression elseExp, Type type) =>