支付模块，调通对 ping++ 的调用，以实现模拟支付。

当然，整体代码还是有点乱，后面花点时间重构下~

现在，缺一个异步 MQ 通知业务方订单支付成功

pay/pay-service-impl/src/main/resources/mapper/PayTransactionExtensionMapper.xml

@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
+<mapper namespace="cn.iocoder.mall.pay.dao.PayTransactionExtensionMapper">
+
+    <sql id="FIELDS">
+        id, transaction_id, pay_channel, transaction_code, extension_data,
+        create_ip, status, create_time
+    </sql>
+
+    <insert id="insert" parameterType="PayTransactionExtensionDO" useGeneratedKeys="true" keyColumn="id" keyProperty="id">
+        INSERT INTO transaction_extension (
+            transaction_id, pay_channel, transaction_code, extension_data,
+            create_ip, status
+        ) VALUES (
+            #{transactionId}, #{payChannel}, #{transactionCode}, #{extensionData},
+            #{createIp}, #{status}
+        )
+    </insert>
+
+    <update id="update">
+        UPDATE transaction_extension
+        <set>
+            <if test="entity.extensionData != null">
+                , extension_data = #{entity.extensionData}
+            </if>
+            <if test="entity.status != null">
+                , status = #{entity.status}
+            </if>
+        </set>
+        WHERE id = #{entity.id}
+        <if test="whereStatus != null">
+            AND status = #{whereStatus}
+        </if>
+    </update>
+
+    <select id="selectByTransactionCode" parameterType="String" resultType="PayTransactionExtensionDO">
+        SELECT
+            <include refid="FIELDS"/>
+        FROM transaction_extension
+        WHERE transaction_code = #{transactionCode}
+        LIMIT 1
+    </select>
+
+</mapper>