- 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

Author: 28810

FreeSql.Tests/FreeSql.Tests/SqlServer/SqlServerExpression/StringTest.cs

@@ -66,6 +66,24 @@ public void Equals__()
             list.Add(select.Where(a => a.TitleVarchar == "aaa").ToList());
         }
 
+        [Fact]
+        public void StringJoin()
+        {
+            var fsql = g.sqlserver;
+            fsql.Delete<StringJoin01>().Where("1=1").ExecuteAffrows();
+            fsql.Insert(new[] { new StringJoin01 { name = "北京" }, new StringJoin01 { name = "上海" }, new StringJoin01 { name = "深圳" }, }).ExecuteAffrows();
+
+            var val1 = string.Join(",", fsql.Select<StringJoin01>().ToList(a => a.name)) + ",";
+            var val2 = fsql.Select<StringJoin01>().ToList(a => string.Join(",", fsql.Select<StringJoin01>().As("b").ToList(b => b.name)));
+            Assert.Equal(val1, val2[0]);
+        }
+        class StringJoin01
+        {
+            [Column(IsIdentity = true)]
+            public int id { get; set; }
+            public string name { get; set; }
+        }
+
         [Fact]
         public void First()
         {

FreeSql/Extensions/FreeSqlGlobalExpressionCallExtensions.cs

@@ -114,6 +114,18 @@ public static class SqlExt
         /// <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 @@ internal static bool IsParameter(this Expression exp)
             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

Providers/FreeSql.Provider.SqlServer/SqlServerExpression.cs

@@ -283,6 +283,24 @@ public override string ExpressionLambdaToSqlCallString(MethodCallExpression exp,
                             return $"'+{_common.IsNull($"cast({ExpressionLambdaToSql(a, tsc)} as nvarchar(max))", "''")}+{nchar}'";
                         }).ToArray();
                         return string.Format(expArgs0, expArgs);
+                    case "Join":
+                        if (exp.IsStringJoin(out var joinExpArgs1, out var joinExpArgs1Args0))
+                        {
+                            var newToListArgs0 = Expression.Call(joinExpArgs1.Object, joinExpArgs1.Method,
+                                Expression.Lambda(
+                                    Expression.Call(
+                                        typeof(string).GetMethod("Concat", new[] { typeof(object), typeof(object) }),
+                                        Expression.Convert(joinExpArgs1Args0.Body, typeof(object)),
+                                        Expression.Convert(exp.Arguments[0], typeof(object))),
+                                    joinExpArgs1Args0.Parameters));
+                            var newToListSql = getExp(newToListArgs0);
+                            if (string.IsNullOrEmpty(newToListSql) == false && newToListSql.StartsWith("(") && newToListSql.EndsWith(")"))
+                            {
+                                newToListSql = $"{newToListSql.Substring(0, newToListSql.Length - 1)} FOR XML PATH(''))";
+                                return newToListSql;
+                            }
+                        }
+                        break;
                 }
             }
             else