Mybatis Practical Article (iii) parameter processing

Mybatis Practical Article (iii) parameter processing

The parameter parametertype in the SQL statement can be omitted from the write.

I. Parameter encapsulation 1.1 single parameter processing

public interface UserMapper {    User getUser(int id);}

The value of #{} in SQL can be arbitrary, mybatis do not do any processing, eg:

<select id="getUser" parameterType="int" resultType="User">    select * from user where id=#{xxx};</select>

1.2 + parameter Handling

Multiple parameters MyBatis encapsulated into a Map, the default parameter of key is param1, param2 ..., you can also use the @Param ("id") to specify the value of key

User getUser(@Param("id") int id, String name);

SQL can have the following wording:

<select id="getUser" resultType="User">    <!--select * from user where id=#{0} and name=#{1};-->    <!--select * from user where id=#{param1} and name=#{param2};-->    <!--select * from user where id=#{0} and name=#{param2};-->    select * from user where id=#{id} and name=#{param2};</select>

1.3 Java Bean

User getUser(User user);

SQL can have the following wording:

<select id="getUser" resultType="User">    select * from user where id=#{id} and name=#{name};</select>

1.4 Map

User getUser(User user);

SQL can have the following wording:

<select id="getUser" resultType="User">    select * from user where id=#{id} and name=#{name};</select>

Thinking:

User getUser(@Param("id") int id, String name);id ==> #{id/param1/0}   name ==> #{param2/1}User getUser(int id, @Param("user") User user);id ==> #{id/param1/0}   name ==> #{param2.name/user.name}# Collection ==> list, Array ==> array. eg: 取出 list 中的第一个值User getUser(List<User> users);id ==> #{list[0]}

Two, #{} and ${} differences

#{}Precompiled, and ${} only string stitching.

In actual work, try to use #{}, special occasions need to use ${}, such as:

select * from ${tablename}

Three, #{} parameters

The MyBatis value is null when the default corresponds to TYPES in the database. Ohter, you can modify the global configuration:

• {Email, javatype=null}

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Mybatis Practical Article (iii) parameter processing