在MongoDB中按几个数组元素过滤？
为此，可以使用$elemMatch运算符。$elemMatch运算符匹配包含一个数组字段的文档，该数组字段的至少一个元素与所有指定的查询条件匹配。首先让我们创建一个包含文档的集合-
> db.filterBySeveralElementsDemo.insertOne(
"_id":100,
"StudentDetails": [
{
"StudentName": "John",
"StudentCountryName": "US",
},
{
"StudentName": "Carol",
"StudentCountryName": "UK"
}
]
}
);
{ "acknowledged" : true, "insertedId" : 100 }
> db.filterBySeveralElementsDemo.insertOne(
{
"_id":101,
"StudentDetails": [
{
"StudentName": "Sam",
"StudentCountryName": "AUS",
},
{
"StudentName": "Chris",
"StudentCountryName": "US"
}
]
}
);
{ "acknowledged" : true, "insertedId" : 101 }以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.filterBySeveralElementsDemo.find().pretty();
这将产生以下输出-
{
"_id" : 100,
"StudentDetails" : [
{
"StudentName" : "John",
"StudentCountryName" : "US"
},
{
"StudentName" : "Carol",
"StudentCountryName" : "UK"
}
]
}
{
"_id" : 101,
"StudentDetails" : [
{
"StudentName" : "Sam",
"StudentCountryName" : "AUS"
},
{
"StudentName" : "Chris",
"StudentCountryName" : "US"
}
]
}以下是按几个数组元素过滤的查询-
> db.filterBySeveralElementsDemo.find({ StudentDetails: { $elemMatch: { StudentName: 'Sam', StudentCountryName: 'AUS' }}}).pretty();这将产生以下输出-
{
"_id" : 101,
"StudentDetails" : [
{
"StudentName" : "Sam",
"StudentCountryName" : "AUS"
},
{
"StudentName" : "Chris",
"StudentCountryName" : "US"
}
]
}