- 增加 lambda 表达式树解析子查询 ToList + string.Join() 产生 类似 group_concat 的效果（适配了 sqlserver/pgsql/oracle/mysql/sqlite/达梦/金仓) #405；

FreeSql/Extensions/FreeSqlGlobalExpressionCallExtensions.cs

@@ -269,5 +269,41 @@ namespace FreeSql
         }
         public interface IGroupConcat { }
         #endregion
+
+        #region string.Join 反射处理，此块代卖用于反射，所以别修改定义
+        public static string StringJoinSqliteGroupConcat(object column, object delimiter)
+        {
+            expContext.Result = $"group_concat({expContext.ParsedContent["column"]},{expContext.ParsedContent["delimiter"]})";
+            return null;
+        }
+        public static string StringJoinPgsqlGroupConcat(object column, object delimiter)
+        {
+            expContext.Result = $"string_agg(({expContext.ParsedContent["column"]})::text,{expContext.ParsedContent["delimiter"]})";
+            return null;
+        }
+        public static string StringJoinMySqlGroupConcat(object column, object delimiter)
+        {
+            expContext.Result = $"group_concat({expContext.ParsedContent["column"]} separator {expContext.ParsedContent["delimiter"]})";
+            return null;
+        }
+        public static string StringJoinOracleGroupConcat(object column, object delimiter)
+        {
+            string orderby = null;
+            var subSelect = expContext._tsc?.subSelect001;
+            if (subSelect != null)
+            {
+                orderby = subSelect?._orderby?.Trim('\r', '\n');
+                if (string.IsNullOrEmpty(orderby))
+                {
+                    var subSelectTb1 = subSelect._tables.FirstOrDefault();
+                    if (subSelectTb1 != null && subSelectTb1.Table.Primarys.Any() == true)
+                        orderby = $"order by {string.Join(",", subSelectTb1.Table.Primarys.Select(a => $"{subSelectTb1.Alias}.{subSelect._commonUtils.QuoteSqlName(a.Attribute.Name)}"))}";
+                }
+            }
+            if (string.IsNullOrEmpty(orderby)) orderby = "order by 1";
+            expContext.Result = $"listagg(to_char({expContext.ParsedContent["column"]}),{expContext.ParsedContent["delimiter"]}) within group({orderby})";
+            return null;
+        }
+        #endregion
     }
 }

FreeSql/Extensions/LambadaExpressionExtensions.cs

@@ -234,23 +234,28 @@ namespace System.Linq.Expressions
             return test.Result;
         }
 
-        public static bool IsStringJoin(this MethodCallExpression exp, out MethodCallExpression joinExpArgs1Out, out LambdaExpression joinExpArgs1Args0Out)
+        static ConcurrentDictionary<Type, ConcurrentDictionary<string, MethodInfo>> _dicTypeMethod = new ConcurrentDictionary<Type, ConcurrentDictionary<string, MethodInfo>>();
+        public static bool IsStringJoin(this MethodCallExpression exp, out Expression tolistObjectExpOut, out MethodInfo toListMethodOut, out LambdaExpression toListArgs0Out)
         {
             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)
+                exp.Arguments[1] is MethodCallExpression toListMethod &&
+                toListMethod.Method.Name == "ToList" &&
+                toListMethod.Arguments.Count == 1 &&
+                toListMethod.Arguments[0] is UnaryExpression joinExpArgs1Args0Tmp &&
+                joinExpArgs1Args0Tmp.Operand is LambdaExpression toListArgs0)
             {
-                joinExpArgs1Out = joinExpArgs1;
-                joinExpArgs1Args0Out = joinExpArgs1Args0;
+                tolistObjectExpOut = toListMethod.Object;
+                toListMethodOut = toListMethod.Type.GetGenericArguments().FirstOrDefault() == typeof(string) ?
+                    toListMethod.Method :
+                    toListMethod.Method.GetGenericMethodDefinition().MakeGenericMethod(typeof(string));
+                toListArgs0Out = toListArgs0;
                 return true;
             }
-            joinExpArgs1Out = null;
-            joinExpArgs1Args0Out = null;
+            tolistObjectExpOut = null;
+            toListMethodOut = null;
+            toListArgs0Out = null;
             return false;
         }
     }