fix nested where bug

Author: ahmad-moussawi

QueryBuilder.Tests/QueryBuilderTest.cs

@@ -336,5 +336,15 @@ public void CombineRawWithPlaceholders()
             Assert.Equal("(SELECT * FROM [Mobiles]) UNION ALL SELECT * FROM [Devices]", c[0]);
             Assert.Equal("(SELECT * FROM `Mobiles`) UNION ALL SELECT * FROM `Devices`", c[1]);
         }
+
+        [Fact]
+        public void NestedEmptyWhere()
+        {
+            var query = new Query("A").Where(q => new Query().Where(q2 => new Query().Where(q3 => new Query())));
+
+            var c = Compile(query);
+
+            Assert.Equal("SELECT * FROM [A]", c[0]);
+        }
     }
 }

QueryBuilder/Compilers/Compiler.Conditions.cs

@@ -115,6 +115,11 @@ protected virtual string CompileNestedCondition<Q>(NestedCondition<Q> x) where Q
             var sql = CompileConditions(x.Query.GetComponents<AbstractCondition>("where", EngineCode));
             var op = x.IsNot ? "NOT " : "";
 
+            if (string.IsNullOrEmpty(sql))
+            {
+                return "";
+            }
+
             return $"{op}({sql})";
         }
 

QueryBuilder/Compilers/Compiler.cs

@@ -484,7 +484,12 @@ protected virtual string CompileWheres(Query query)
             }
 
             var conditions = query.GetComponents<AbstractCondition>("where", EngineCode);
-            var sql = CompileConditions(conditions);
+            var sql = CompileConditions(conditions).Trim();
+
+            if (string.IsNullOrEmpty(sql))
+            {
+                return null;
+            }
 
             return $"WHERE {sql}";
         }