MongoDB-elemMatch

$elemMatch 是用来匹配数组内的元素的。

与 . 容易产生混淆。

$elemMatch 与 . 对比

初始化源数据

db.em.insert({"arr":[{"e1":"a","e2":11},{"e1":"b","e2":12},{"e1":"c","e2":13},{"e1":"d","e2":14}]})
db.em.insert({"arr":[{"e1":"a","e2":21},{"e1":"b","e2":22},{"e1":"c","e2":23},{"e1":"d","e2":24}]})
db.em.insert({"arr":[{"e1":"a","e2":31},{"e1":"b","e2":32},{"e1":"c","e2
":33},{"e1":"d","e2":34}]})
db.em.insert({"arr":[{"e1":"a","e2":41},{"e1":"b","e2":42},{"e1":"c","e2":43},{"e1":"d","e2":44}]})
db.em.insert({"arr":[{"e1":"a","e2":51},{"e1":"b","e2":52},{"e1":"c","e2":53},{"e1":"d","e2":54}]})

用 . 查询

db.em.find({"arr":{$elemMatch: {"e1":"a","e2":32}}})

无结果集

用 $elemMatch 查询

db.em.find({"arr.e1":"a","arr.e2":32})

查询结果如下：

总结

• $elemMatch：数组内单个元素匹配则符合
• .：数组内多个元素能分别匹配上条件即符合