Use of Wrapper in Mybatis-plus

A list,

In the previous section, we mentioned that when CRUD operations are performed, they can be obtained by passing an UpdateWrapper or QueryWrapper as a condition for updating or querying the operations. In this section, we will show you how to use these two types of wrappers.

The parent classes of QueryWrapper(LambdaQueryWrapper) and UpdateWrapper(LambdaUpdateWrapper) are used to generate SQL where conditions, The Entity attribute is also used to generate SQL WHERE conditions

Second, the AbstractWrapper

Unified description of parameters:

• Boolean condition: indicates whether the condition is added to the final GENERATED SQL.

  For example, query.eq(stringutils.isNotblank (name), Entity::getName, name), this eq is not generated in the WHERE condition when name is empty;

• Null2IsNull: Whether to add a parameter to the WHERE condition when the value of Map in the parameter is null:

  Such as:

  Default: allEq({id:1,name:” Lao Wang “,age:null})–>id = 1 and name = ‘Lao Wang’ and age is null

  Null2IsNull == false: allEq({id:1,name:” Lao Wang “,age:null}, false)– >id = 1 and name = ‘Lao Wang’

Used to generate a WHERE condition:

Third, QueryWrapper

Select Sets the query fields

select(String... sqlSelect)
select(Predicate<TableFieldInfo> predicate)
select(Class<T> entityClass, Predicate<TableFieldInfo> predicate)
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The second and third usages can be used to exclude fields in the case of multiple fields, for example:

queryWrapper.select(info -> info.getProperty().startsWith("test"));
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queryWrapper.select(User.class, info->! info.getColumn() .equals("email") && !info.getColumn().equals("create_time"));
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Four, UpdateWrapper

1. SET the SET field

set(String column, Object val)
set(boolean condition, String column, Object val)
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• Ex. :Set ("name", "Lao Li Tou ")
• Ex. :set("name", "")–> The database field value changesAn empty string
• Ex. :set("name", null)–> The database field value changesnull

2. SET the SET SQL

setSql(String sql)
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Example :setSql(“name = ‘old’ header ‘”)