Shulou(Shulou.com)06/03 Report--

In this issue, the editor will bring you about how the MyBatis insert statement returns the primary key and selectKey tags. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

The insert statement returns the primary key and selectKey tag

After inserting a record into the database, sometimes we need the primary key of the record for subsequent operations.

If you check the database again after insertion, it is obviously not elegant and efficient. MyBatis already has the function of returning the primary key after insert. Here are the specific methods for several different situations.

1. The case of a self-increasing primary key

For databases like MySQL and Sql Server that support self-incrementing primary keys, you can set useGeneratedKeys= "true" and keyProperty. For example, there is a table tbl_employee with four fields of id,name,age,create_time, which can be written as follows in the MyBatis mapping file:

INSERT INTO tbl_employee (name, age, create_time) VALUES (# {name}, # {age}, # {createTime})

UseGeneratedKeys= "true": use an automatically generated primary key

KeyProperty: specifies which attribute the primary key is (of javaBean).

UseGeneratedKeys:

(insert and update only) This tells MyBatis to use the JDBC getGeneratedKeys method to retrieve keys generated internally by the database (e.g.auto increment fields in RDBMS like MySQL or SQL Server). Default: false

KeyProperty:

(insert and update only) Identifies a property into which MyBatis will set the key value returned by getGeneratedKeys, or by a selectKey child element of the insert statement. Default: unset.

Can be a comma separated list of property names if multiple generated columns are expected.

Using Sequence to get the primary key in 2.Oracle

For the Oracle database, you need to use Sequence when you want to use self-incrementing fields. Suppose we have now created a Sequence named SEQ_ADMIN, which can be used in conjunction with the selectKey tag in the mapping file in MyBatis.

SELECT SEQ_ADMIN.NEXTVAL FROM DUAL INSERT INTO tbl_employee (id, name, age, create_time) VALUES (# {id}, # {name}, # {age}, # {createTime})

Order= "BEFORE" means that SELECT SEQ_ADMIN.NEXTVAL FROM DUAL assigns a value to id before the INSERT statement is executed. Conversely, order can also be set to AFTER, which means that after the INSERT statement is executed, the statement in the slectKey tag is queried again and assigned to that attribute of Javabean's keyProperty.

Source code analysis

From the point of view of the source code, generateKeys is generated in BaseStatementHandler, mainly for execution:

Protected void generateKeys (Object parameter) {KeyGenerator keyGenerator = mappedStatement.getKeyGenerator (); ErrorContext.instance (). Store (); keyGenerator.processBefore (executor, mappedStatement, null, parameter); ErrorContext.instance (). Recall ();}

ProcessBefore, indicates pre-processing. Corresponding to the order= "BEFORE" attribute in selectKey in mapper, the query key is executed and set to the parameter object.

In each declaration processor, update has code:

KeyGenerator keyGenerator = mappedStatement.getKeyGenerator (); keyGenerator.processAfter (executor, mappedStatement, ps, parameterObject)

ProcessAfter, which means to perform post-processing, corresponds to the order= "AFTER" attribute in selectKey in mapper, which means that after execution, check the key again and set it to the parameter object.

The generation and return of the MyBatis insert statement key. Use the generator insert into user (user_name) values (# {userName}) that comes with the database

Mybatis takes the automatically generated columns from the database and assigns values to the userId property of the passed-in parameters.

two。 Use selectKey insert into user (user_name) values (# {userName}) SELECT LAST_INSERT_ID ()

The selectKey statement is executed after the insert statement, and the return value is stuffed into the userId property of the incoming parameter.

Insert into user (user_name) values (# {userName}) SELECT LAST_INSERT_ID ()

First execute the selectKey and assign the return value to the userId property of the incoming parameter, and then execute the insert statement.

This is how the MyBatis insert statement shared by the editor returns the primary key and selectKey tags. If you happen to have similar doubts, please refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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