- 增加 SqlServer lambda 表达式树解析子查询 ToList + string.Join() 产生 类似 group_concat 的效果；#405

FreeSql/Extensions/FreeSqlGlobalExpressionCallExtensions.cs

@@ -114,6 +114,18 @@ namespace FreeSql
         /// <param name="column"></param>
         /// <returns></returns>
         public static IGroupConcat GroupConcat(object column) => SqlExtExtensions.GroupConcat(column);
+
+        /// <summary>
+        /// PostgreSQL string_agg(.., ..)
+        /// </summary>
+        /// <param name="column"></param>
+        /// <param name="delimiter"></param>
+        /// <returns></returns>
+        public static string StringAgg(object column, object delimiter)
+        {
+            expContext.Value.Result = $"string_agg({expContext.Value.ParsedContent["column"]}, {expContext.Value.ParsedContent["delimiter"]})";
+            return "";
+        }
     }
 
     [ExpressionCall]

FreeSql/Extensions/LambadaExpressionExtensions.cs

@@ -233,6 +233,26 @@ namespace System.Linq.Expressions
             test.Visit(exp);
             return test.Result;
         }
+
+        public static bool IsStringJoin(this MethodCallExpression exp, out MethodCallExpression joinExpArgs1Out, out LambdaExpression joinExpArgs1Args0Out)
+        {
+            if (exp.Arguments.Count == 2 &&
+                exp.Arguments[1].NodeType == ExpressionType.Call &&
+                exp.Arguments[1].Type.FullName.StartsWith("System.Collections.Generic.List`1") &&
+                exp.Arguments[1] is MethodCallExpression joinExpArgs1 &&
+                joinExpArgs1.Method.Name == "ToList" &&
+                joinExpArgs1.Arguments.Count == 1 &&
+                joinExpArgs1.Arguments[0] is UnaryExpression joinExpArgs1Args0Tmp &&
+                joinExpArgs1Args0Tmp.Operand is LambdaExpression joinExpArgs1Args0)
+            {
+                joinExpArgs1Out = joinExpArgs1;
+                joinExpArgs1Args0Out = joinExpArgs1Args0;
+                return true;
+            }
+            joinExpArgs1Out = null;
+            joinExpArgs1Args0Out = null;
+            return false;
+        }
     }
 
     internal class NewExpressionVisitor : ExpressionVisitor