Merge pull request #618 from sqlkata/iss-581_where_exists_remove_select

Iss 581 where exists remove select

Author: ahmad-moussawi

QueryBuilder.Tests/SelectTests.cs

@@ -903,5 +903,33 @@ public void SelectWithFilter()
             Assert.Equal("SELECT [Title], SUM(CASE WHEN [Published_Month] = 'Jan' THEN [ViewCount] END) AS [Published_Jan], SUM(CASE WHEN [Published_Month] = 'Feb' THEN [ViewCount] END) AS [Published_Feb] FROM [Posts]", sqlServer.ToString());
         }
 
+        [Fact]
+        public void SelectWithExists()
+        {
+            var q = new Query("Posts").WhereExists(
+                new Query("Comments").WhereColumns("Comments.PostId", "=", "Posts.Id")
+            );
+
+            var sqlServer = Compilers.CompileFor(EngineCodes.SqlServer, q);
+            Assert.Equal("SELECT * FROM [Posts] WHERE EXISTS (SELECT 1 FROM [Comments] WHERE [Comments].[PostId] = [Posts].[Id])", sqlServer.ToString());
+        }
+
+        [Fact]
+        public void SelectWithExists_OmitSelectIsFalse()
+        {
+            var q = new Query("Posts").WhereExists(
+                new Query("Comments").Select("Id").WhereColumns("Comments.PostId", "=", "Posts.Id")
+            );
+
+
+            var compiler = new SqlServerCompiler
+            {
+                OmitSelectInsideExists = false,
+            };
+
+            var sqlServer = compiler.Compile(q).ToString();
+            Assert.Equal("SELECT * FROM [Posts] WHERE EXISTS (SELECT [Id] FROM [Comments] WHERE [Comments].[PostId] = [Posts].[Id])", sqlServer.ToString());
+        }
+
     }
 }

QueryBuilder/Base.Where.cs

@@ -539,10 +539,6 @@ public Q WhereExists(Query query)
                 throw new ArgumentException($"'{nameof(FromClause)}' cannot be empty if used inside a '{nameof(WhereExists)}' condition");
             }
 
-            // remove unneeded components
-            query = query.Clone().ClearComponent("select")
-                .SelectRaw("1");
-
             return AddComponent("where", new ExistsCondition
             {
                 Query = query,

QueryBuilder/Compilers/Compiler.Conditions.cs

@@ -247,7 +247,16 @@ protected virtual string CompileExistsCondition(SqlResult ctx, ExistsCondition i
         {
             var op = item.IsNot ? "NOT EXISTS" : "EXISTS";
 
-            var subCtx = CompileSelectQuery(item.Query);
+
+            // remove unneeded components
+            var query = item.Query.Clone();
+
+            if (OmitSelectInsideExists)
+            {
+                query.ClearComponent("select").SelectRaw("1");
+            }
+
+            var subCtx = CompileSelectQuery(query);
 
             ctx.Bindings.AddRange(subCtx.Bindings);
 

QueryBuilder/Compilers/Compiler.cs

@@ -30,6 +30,12 @@ protected Compiler()
         /// <value></value>            
         public virtual bool SupportsFilterClause { get; set; } = false;
 
+        /// <summary>
+        /// If true the compiler will remove the SELECT clause for the query used inside WHERE EXISTS
+        /// </summary>
+        /// <value></value>            
+        public virtual bool OmitSelectInsideExists { get; set; } = true;
+
         protected virtual string SingleRowDummyTableName { get => null; }
 
         /// <summary>