feat: 添加 Join 查询构建。

mybatis-flex-core/src/main/java/com/mybatisflex/core/activerecord/query/JoinBuilder.java

@@ -0,0 +1,55 @@
+/*
+ *  Copyright (c) 2022-2023, Mybatis-Flex (fuhai999@gmail.com).
+ *  <p>
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *  <p>
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *  <p>
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package com.mybatisflex.core.activerecord.query;
+
+import com.mybatisflex.core.query.CPI;
+import com.mybatisflex.core.query.Join;
+import com.mybatisflex.core.query.QueryCondition;
+import com.mybatisflex.core.query.RawFragment;
+
+/**
+ * Lambda joins 构建器。
+ *
+ * @author 王帅
+ * @since 2023-07-28
+ */
+public class JoinBuilder<R extends QueryModel<R>> {
+
+    private final R queryModel;
+    private final Join join;
+
+    public JoinBuilder(R queryModel, Join join) {
+        this.queryModel = queryModel;
+        this.join = join;
+    }
+
+    public JoinBuilder<R> as(String alias) {
+        CPI.getJoinQueryTable(join).as(alias);
+        return this;
+    }
+
+    public R on(String on) {
+        join.on(new RawFragment(on));
+        return queryModel;
+    }
+
+    public R on(QueryCondition on) {
+        join.on(on);
+        return queryModel;
+    }
+
+}