一、引言

那麼那麼那麼今天來說下MP中強大的條件查詢功能。

本章是基於上個案例來講的：MyBaits-Plus 快速入門案例

二、具體操作

首先來說說基本的查詢吧，根據主鍵或者簡單的查詢條件進行查詢。

  /**
   * 通過單個ID主鍵進行查詢
   */
  @Test
  public void selectById() {
    User user = userMapper.selectById(1094592041087729666L);
    System.out.println(user);
  }

  /**
   * 通過多個ID主鍵查詢
   */
  @Test
  public void selectByList() {
    List<Long> longs = Arrays.asList(1094592041087729666L,1094590409767661570L);
    List<User> users = userMapper.selectBatchIds(longs);
    users.forEach(System.out::println);
  }

  /**
   * 通過Map引數進行查詢
   */
  @Test
  public void selectByMap() {
    Map<String,Object> params = new HashMap<>();
    params.put("name","張雨琪");
    List<User> users = userMapper.selectByMap(params);
    users.forEach(System.out::println);
  }

MyBatis-Plus還提供了Wrapper條件構造器，具體使用看如下程式碼：

/**
   * 名字包含雨並且年齡小於40
   * <p>
   * WHERE name LIKE '%雨%' AND age < 40
   */
  @Test
  public void selectByWrapperOne() {
    QueryWrapper<User> wrapper = new QueryWrapper();
    wrapper.like("name","雨").lt("age",40);
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
  }

  /**
   * 名字包含雨
   * 年齡大於20小於40
   * 郵箱不能為空
   * <p>
   * WHERE name LIKE '%雨%' AND age BETWEEN 20 AND 40 AND email IS NOT NULL
   */
  @Test
  public void selectByWrapperTwo() {
    QueryWrapper<User> wrapper = Wrappers.query();
    wrapper.like("name","雨").between("age",20,40).isNotNull("email");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
  }

  /**
   * 名字為王性
   * 或者年齡大於等於25
   * 按照年齡降序排序，年齡相同按照id升序排序
   * <p>
   * WHERE name LIKE '王%' OR age >= 25 ORDER BY age DESC,id ASC
   */
  @Test
  public void selectByWrapperThree() {
    QueryWrapper<User> wrapper = Wrappers.query();
    wrapper.likeRight("name","王").or()
        .ge("age",25).orderByDesc("age").orderByAsc("id");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
  }

  /**
   * 查詢建立時間為2019年2月14
   * 並且上級領導姓王
   * <p>
   * WHERE date_format(create_time,'%Y-%m-%d') = '2019-02-14' AND manager_id IN (select id from user where name like '王%')
   */
  @Test
  public void selectByWrapperFour() {
    QueryWrapper<User> wrapper = Wrappers.query();
    wrapper.apply("date_format(create_time,'%Y-%m-%d') = {0}","2019-02-14")
        .inSql("manager_id","select id from user where name like '王%'");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
  }

  /**
   * 查詢王姓
   * 並且年齡小於40或者郵箱不為空
   * <p>
   * WHERE name LIKE '王%' AND ( age < 40 OR email IS NOT NULL )
   */
  @Test
  public void selectByWrapperFive() {
    QueryWrapper<User> wrapper = Wrappers.query();
    wrapper.likeRight("name","王").and(qw -> qw.lt("age",40).or().isNotNull("email"));
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
  }

  /**
   * 查詢王姓
   * 並且年齡大於20 、年齡小於40、郵箱不能為空
   * <p>
   * WHERE name LIKE ? OR ( age BETWEEN ? AND ? AND email IS NOT NULL )
   */
  @Test
  public void selectByWrapperSix() {
    QueryWrapper<User> wrapper = Wrappers.query();
    wrapper.likeRight("name","王").or(
        qw -> qw.between("age",40).isNotNull("email")
    );
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
  }

  /**
   * (年齡小於40或者郵箱不為空) 並且名字姓王
   * WHERE ( age < 40 OR email IS NOT NULL ) AND name LIKE '王%'
   */
  @Test
  public void selectByWrapperSeven() {
    QueryWrapper<User> wrapper = Wrappers.query();
    wrapper.nested(qw -> qw.lt("age",40).or().isNotNull("email"))
        .likeRight("name","王");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
  }

  /**
   * 查詢年齡為30、31、32
   * WHERE age IN (?,?,?)
   */
  @Test
  public void selectByWrapperEight() {
    QueryWrapper<User> wrapper = Wrappers.query();
    wrapper.in("age",Arrays.asList(30,31,32));
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
  }

  /**
   * 查詢一條資料
   * limit 1
   */
  @Test
  public void selectByWrapperNine() {
    QueryWrapper<User> wrapper = Wrappers.query();
    wrapper.in("age",32)).last("limit 1");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
  }

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