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本文大约4311字,预计阅读时长15分钟
前言
距离上一篇文章已经过去一个多月了,最近忙着项目上线,连轴转了一个多月,头发都少了不少!今天分享的是MP入门使用教程的最后的部分,也是使用的比较多的地方,就是如何使用MP进行条件查询!
正文
本文是在前两篇文章的基础之上进行拓展,所以如果有不清楚的可以先参考前面的两篇文章:SpringBoot系列:MybatisPlus的入门级使用教程(上),以及SpringBoot系列:MybatisPlus的入门级使用教程(中),源码地址会放在最后。
先来看一个使用MP进行条件查询的例子:
//构造条件构造器
QueryWrapper<User> wrapper = new QueryWrapper<>();
//构造条件
wrapper.eq("User_ID",ID);
//使用提供的selectList默认方法进行结果查询
List<EduChapter> userList = baseMapper.selectList(wrapper);
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上述代码中首先使用QuerWrapper构造一个条件构造器,类型是需要查询的实体类User,然后使用条件构造器组装查询条件,上面是userid等于id,然后使用mp提供的默认的查询结果的selectList方法进行查询,条件就是上面构造的条件。
看起来很简单,这里主要就是使用QuerWrapper条件构造器构造查询条件,然后作为参数传入查询方法中即可。
接下来看看QuerWrapper的源码,源码比较长,这里截取部分,有需要的可以自行查看:
public class QueryWrapper<T> extends AbstractWrapper<T, String, QueryWrapper<T>> {
.....
}
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可以发现这里QueryWrapper继承了AbstractWrapper抽象类,点进去看看AbstractWrapper抽象类的源码:
public abstract class AbstractWrapper<T, R, This extends AbstractWrapper<T, R, This>> extends Wrapper<T> implements Compare<This, R>, Nested<This>, Join<This>, Func<This, R> {
private static final String MP_GENERAL_PARAMNAME = "MPGENVAL";
private static final String DEFAULT_PARAM_ALIAS = "ew";
private static final String PLACE_HOLDER = "{%s}";
private static final String MYBATIS_PLUS_TOKEN = "#{%s.paramNameValuePairs.%s}";
protected final This typedThis = this;
protected AtomicInteger paramNameSeq;
protected Map<String, Object> paramNameValuePairs;
protected String paramAlias = null;
protected String lastSql = "";
protected T entity;
protected MergeSegments expression;
protected Class<T> entityClass;
public AbstractWrapper() {
}
public T getEntity() {
return this.entity;
}
public This setEntity(T entity) {
this.entity = entity;
this.initEntityClass();
return this.typedThis;
}
protected void initEntityClass() {
if (this.entity != null) {
this.entityClass = this.entity.getClass();
}
}
protected Class<T> getCheckEntityClass() {
Assert.notNull(this.entityClass, "entityClass must not null,please set entity before use this method!");
return this.entityClass;
}
public <V> This allEq(boolean condition, Map<R, V> params, boolean null2IsNull) {
if (condition && CollectionUtils.isNotEmpty(params)) {
params.forEach((k, v) -> {
if (StringUtils.checkValNotNull(v)) {
this.eq(k, v);
} else if (null2IsNull) {
this.isNull(k);
}
});
}
return this.typedThis;
}
public <V> This allEq(boolean condition, BiPredicate<R, V> filter, Map<R, V> params, boolean null2IsNull) {
if (condition && CollectionUtils.isNotEmpty(params)) {
params.forEach((k, v) -> {
if (filter.test(k, v)) {
if (StringUtils.checkValNotNull(v)) {
this.eq(k, v);
} else if (null2IsNull) {
this.isNull(k);
}
}
});
}
return this.typedThis;
}
public This eq(boolean condition, R column, Object val) {
return this.addCondition(condition, column, SqlKeyword.EQ, val);
}
public This ne(boolean condition, R column, Object val) {
return this.addCondition(condition, column, SqlKeyword.NE, val);
}
public This gt(boolean condition, R column, Object val) {
return this.addCondition(condition, column, SqlKeyword.GT, val);
}
public This ge(boolean condition, R column, Object val) {
return this.addCondition(condition, column, SqlKeyword.GE, val);
}
public This lt(boolean condition, R column, Object val) {
return this.addCondition(condition, column, SqlKeyword.LT, val);
}
public This le(boolean condition, R column, Object val) {
return this.addCondition(condition, column, SqlKeyword.LE, val);
}
public This like(boolean condition, R column, Object val) {
return this.doIt(condition, () -> {
return this.columnToString(column);
}, SqlKeyword.LIKE, () -> {
return this.formatSql("{0}", "%" + val + "%");
});
}
public This notLike(boolean condition, R column, Object val) {
return this.not(condition).like(condition, column, val);
}
public This likeLeft(boolean condition, R column, Object val) {
return this.doIt(condition, () -> {
return this.columnToString(column);
}, SqlKeyword.LIKE, () -> {
return this.formatSql("{0}", "%" + val);
});
}
public This likeRight(boolean condition, R column, Object val) {
return this.doIt(condition, () -> {
return this.columnToString(column);
}, SqlKeyword.LIKE, () -> {
return this.formatSql("{0}", val + "%");
});
}
public This between(boolean condition, R column, Object val1, Object val2) {
return this.doIt(condition, () -> {
return this.columnToString(column);
}, SqlKeyword.BETWEEN, () -> {
return this.formatSql("{0}", val1);
}, SqlKeyword.AND, () -> {
return this.formatSql("{0}", val2);
});
}
public This notBetween(boolean condition, R column, Object val1, Object val2) {
return this.not(condition).between(condition, column, val1, val2);
}
public This and(boolean condition, Function<This, This> func) {
return this.and(condition).addNestedCondition(condition, func);
}
public This or(boolean condition, Function<This, This> func) {
return this.or(condition).addNestedCondition(condition, func);
}
public This nested(boolean condition, Function<This, This> func) {
return this.addNestedCondition(condition, func);
}
public This or(boolean condition) {
return this.doIt(condition, SqlKeyword.OR);
}
public This apply(boolean condition, String applySql, Object... value) {
return this.doIt(condition, WrapperKeyword.APPLY, () -> {
return this.formatSql(applySql, value);
});
}
public This last(boolean condition, String lastSql) {
if (condition) {
this.lastSql = " " + lastSql;
}
return this.typedThis;
}
public This exists(boolean condition, String existsSql) {
return this.doIt(condition, SqlKeyword.EXISTS, () -> {
return String.format("(%s)", existsSql);
});
}
public This notExists(boolean condition, String notExistsSql) {
return this.not(condition).exists(condition, notExistsSql);
}
public This isNull(boolean condition, R column) {
return this.doIt(condition, () -> {
return this.columnToString(column);
}, SqlKeyword.IS_NULL);
}
public This isNotNull(boolean condition, R column) {
return this.doIt(condition, () -> {
return this.columnToString(column);
}, SqlKeyword.IS_NOT_NULL);
}
public This in(boolean condition, R column, Collection<?> value) {
return CollectionUtils.isEmpty(value) ? this.typedThis : this.doIt(condition, () -> {
return this.columnToString(column);
}, SqlKeyword.IN, this.inExpression(value));
}
public This notIn(boolean condition, R column, Collection<?> value) {
return CollectionUtils.isEmpty(value) ? this.typedThis : this.not(condition).in(condition, column, value);
}
public This inSql(boolean condition, R column, String inValue) {
return this.doIt(condition, () -> {
return this.columnToString(column);
}, SqlKeyword.IN, () -> {
return String.format("(%s)", inValue);
});
}
public This notInSql(boolean condition, R column, String inValue) {
return this.not(condition).inSql(condition, column, inValue);
}
public This groupBy(boolean condition, R... columns) {
return ArrayUtils.isEmpty(columns) ? this.typedThis : this.doIt(condition, SqlKeyword.GROUP_BY, () -> {
return this.columnsToString(columns);
});
}
public This orderBy(boolean condition, boolean isAsc, R... columns) {
if (ArrayUtils.isEmpty(columns)) {
return this.typedThis;
} else {
SqlKeyword mode = isAsc ? SqlKeyword.ASC : SqlKeyword.DESC;
Object[] var5 = columns;
int var6 = columns.length;
for(int var7 = 0; var7 < var6; ++var7) {
R column = var5[var7];
this.doIt(condition, SqlKeyword.ORDER_BY, () -> {
return this.columnToString(column);
}, mode);
}
return this.typedThis;
}
}
public This having(boolean condition, String sqlHaving, Object... params) {
return this.doIt(condition, SqlKeyword.HAVING, () -> {
return this.formatSqlIfNeed(condition, sqlHaving, params);
});
}
protected This not(boolean condition) {
return this.doIt(condition, SqlKeyword.NOT);
}
protected This and(boolean condition) {
return this.doIt(condition, SqlKeyword.AND);
}
protected This addCondition(boolean condition, R column, SqlKeyword sqlKeyword, Object val) {
return this.doIt(condition, () -> {
return this.columnToString(column);
}, sqlKeyword, () -> {
return this.formatSql("{0}", val);
});
}
protected This addNestedCondition(boolean condition, Function<This, This> func) {
return this.doIt(condition, WrapperKeyword.LEFT_BRACKET, (ISqlSegment)func.apply(this.instance(this.paramNameSeq, this.paramNameValuePairs)), WrapperKeyword.RIGHT_BRACKET);
}
protected abstract This instance(AtomicInteger var1, Map<String, Object> var2);
protected final String formatSql(String sqlStr, Object... params) {
return this.formatSqlIfNeed(true, sqlStr, params);
}
protected final String formatSqlIfNeed(boolean need, String sqlStr, Object... params) {
if (need && !StringUtils.isEmpty(sqlStr)) {
if (ArrayUtils.isNotEmpty(params)) {
for(int i = 0; i < params.length; ++i) {
String genParamName = "MPGENVAL" + this.paramNameSeq.incrementAndGet();
sqlStr = sqlStr.replace(String.format("{%s}", i), String.format("#{%s.paramNameValuePairs.%s}", this.getParamAlias(), genParamName));
this.paramNameValuePairs.put(genParamName, params[i]);
}
}
return sqlStr;
} else {
return null;
}
}
private ISqlSegment inExpression(Collection<?> value) {
return () -> {
return (String)value.stream().map((i) -> {
return this.formatSql("{0}", i);
}).collect(Collectors.joining(",", "(", ")"));
};
}
protected final void initNeed() {
this.paramNameSeq = new AtomicInteger(0);
this.paramNameValuePairs = new HashMap(16);
this.expression = new MergeSegments();
}
protected This doIt(boolean condition, ISqlSegment... sqlSegments) {
if (condition) {
this.expression.add(sqlSegments);
}
return this.typedThis;
}
public String getParamAlias() {
return StringUtils.isEmpty(this.paramAlias) ? "ew" : this.paramAlias;
}
public String getSqlSegment() {
String sqlSegment = this.expression.getSqlSegment();
if (StringUtils.isNotEmpty(sqlSegment)) {
return sqlSegment + this.lastSql;
} else {
return StringUtils.isNotEmpty(this.lastSql) ? this.lastSql : null;
}
}
public MergeSegments gt() {
return this.expression;
}
public Map<String, Object> getParamNameValuePairs() {
return this.paramNameValuePairs;
}
protected String columnsToString(R... columns) {
return (String)Arrays.stream(columns).map(this::columnToString).collect(Collectors.joining(","));
}
protected abstract String columnToString(R var1);
public This clone() {
return (AbstractWrapper)SerializationUtils.clone(this.typedThis);
}
}
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AbstractWrapper继承了Wrapper抽象类,并且AbstractWrapper中提供了eq、gt、ge等条件判断方法,以及getExpression()生成条件表达式方法。类以及接口之间的关系如下图:
总结如下:
Wrapper : 它是条件构造抽象类,也是最顶端的父类;
AbstractWrapper : 也是条件构造器抽象类,继承了Wrapper 抽象类,它主要用于查询条件封装,生成 sql 的 where 条件
QueryWrapper : 是条件构造器的实体类,是对各类的Entity对象封装的操作类;
可以发现在AbstractWrapper类中有各类的ge、gt、le、lt、isNull、isNotNull、eq、ne等方法,它们等同于,sql语句中的大于、等于、小于等条件,比如
wrapper.eq("User_ID",ID);
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这行代码就表示,条件是user_ID字段的值等于ID,源码如下:
public This eq(boolean condition, R column, Object val) {
return this.addCondition(condition, column, SqlKeyword.EQ, val);
}
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eq这类的方法的第一个参数是condition表示该条件是否加入生成的sql中,默认以及不写就是true,第二个参数表示的是字段名(注意需要和数据库中的字段名一样),第三个参数就是字段的值。
所以可以发现条件构造器最主要的就是eq、ge、gt这类方法的使用。它们大多数都是一样的,这里简单演示几种:
比如allEq,源码可以参考上面AbstractWrapper的源码:
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
Map<String, Object> map = new HashMap<>();
map.put("id", 2);
map.put("name", "Jack");
map.put("age", 20);
queryWrapper.allEq(map);
List<User> users = userMapper.selectList(queryWrapper);
users.forEach(System.out::println);
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like的使用:
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper
.like("address","上海")
.notLike("name", "e")
.likeRight("email", "t");
List<Map<String, Object>> maps = userMapper.selectMaps(queryWrapper);//返回值是Map列表
maps.forEach(System.out::println);
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or、and的使用:如果不调用or则默认为使用 and
//修改值
User user = new User();
user.setAge(99);
user.setName("Andy");
//修改条件
UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
userUpdateWrapper
.like("name", "h")
.or()
.between("age", 20, 30);
int result = userMapper.update(user, userUpdateWrapper);
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这里使用的是 UpdateWrapper, 它主要用于Update 条件封装,对Entity对象进行更新操作。
还可以使用select方法指定需要查询的字段,这里就是指定查询的id,name,age:
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.select("id", "name", "age");
List<User> users = userMapper.selectList(queryWrapper);
users.forEach(System.out::println);
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set、setSql:
//修改值
User user = new User();
user.setAge(99);
//修改条件
UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
userUpdateWrapper
.like("name", "h")
.set("name", "老李头")//除了可以查询还可以使用set设置修改的字段
.setSql(" email = '[email protected]'");//可以有子查询
int result = userMapper.update(user, userUpdateWrapper);
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最终的sql会合并 user.setAge(),以及 userUpdateWrapper.set() 和 setSql() 中 的字段。等同于:
UPDATE user SET age=99, name="老李头", email = '[email protected]' WHERE deleted=0 AND name LIKE "h"
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总结
以上就是关于mybatisplus的条件构造器的使用,至此mybatisplus的介绍大结局了,要想掌握更多的mp的使用,还是要在日常的开发中多多练习。更多关于mybatisplus的内容可以参考以下内容:
mybatisplus源码地址:
https://gitcode.net/mirrors/baomidou/mybatis-plus?utm_source=csdn_github_accelerator
MP官网地址:
https://baomidou.com/pages/24112f/
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