Querywrapper in mybaits plus

One 、queryWrapper What is it?

queryWrapper yes mybatis plus The object encapsulation operation class that implements query in , His hierarchy is as follows

In the picture above ,

Wrapper ： Conditionally construct abstract classes , Top parent class , Provided in an abstract class 4 There are two ways to display the source code
AbstractWrapper ： Used to encapsulate query conditions , Generate sql Of where Conditions
AbstractLambdaWrapper ： Lambda Grammar use Wrapper Unified processing and parsing lambda obtain column.
LambdaQueryWrapper ： You can see that the name is used for Lambda Query used by syntax Wrapper
LambdaUpdateWrapper ： Lambda Update package Wrapper
QueryWrapper ： Entity Object encapsulates the operation class , Not with lambda grammar
UpdateWrapper ： Update Conditional encapsulation , be used for Entity Object update operation

Two 、 Use demo

  @PostMapping("/login")
    public Result login(@Validated @RequestBody JSONObject jsonObject, HttpServletResponse response) {
    
        User us = jsonObject.toJavaObject(User.class);
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.eq("username",us.getUsername()).eq("password",us.getPassword());
        User user = userService.getOne(queryWrapper);
        Assert.notNull(user, " The user doesn't exist ");

Query the database for a person whose user name and password match those passed in , And encapsulate the results as user

3、 ... and 、QueryWrapper Methods

Four 、 summary

The blog content above is simple , Only one query function is shown . When you actually use it , May, in accordance with the   The methods contained above the condition constructor , Set the conditions for you to query the data , call BaseMapper The corresponding method in