如何从 MyBatis 获取值？

Question

I'm having a problem in retrieving a property from myBatis. It says java.lang.NullPointerException . What I want is to get only the user_id from the result map which is auto generated after using a function to insert values to the database (I'm using oracle 10g).

My code in my mapper is as follows

<resultMap type="User" id="userMap">
    <result property="userId" column="user_id"/>
    <result property="someProperty1" column="property_1"/>
    <result property="someProperty2" column="property_2"/>
</resultMap>

<insert id="addUser" parameterType="map" statementType="CALLABLE">
    { CALL 
    #{userResult, javaType=java.sql.ResultSet, jdbcType=CURSOR, mode=OUT, resultMap=userMap} :=
    PROJECT.create_user(
            #{surname,      javaType=String,    jdbcType=VARCHAR,   mode=IN},
            #{givenName,    javaType=String,    jdbcType=VARCHAR,   mode=IN},
            #{middleName,   javaType=String,    jdbcType=VARCHAR,   mode=IN}    
    )}
</insert>

Here is where the java.lang.NullPointerException occurs

return Integer.parseInt(paramMap.get("userId").toString());

I'm using private Map<String, Object> paramMap = new HashMap<String, Object>(); It seems that I've used paramMap.get("userId") is wrong but I am not sure with this.

Any suggestions or hints would be very helpful! Thanks a lot!

Answer 1

Getting auto-generated keys back from the database has never been standardized, so it tends to be database-specific. With Oracle, you need to first select the new key value from a sequence, do the insert and return the result. This question has the real oil for a MyBatis project.

Some of the more recent Java ER mapping frameworks are handling this transparently. For instance Spring JDBC Template has a GeneratedKeyHolder object that abstracts the database work. See this question for an example.