对于MongoDB,使用时
$lookup
若要查询多个集合,是否可以获取
?
我不想要的是完整对象及其所有键/值的列表。
数据
:
failover_tool:PRIMARY> db.foo.find().pretty()
{
"_id" : ObjectId("5ce72e415267960532b8df09"),
"name" : "foo1",
"desc" : "first foo"
}
{
"_id" : ObjectId("5ce72e4a5267960532b8df0a"),
"name" : "foo2",
"desc" : "second foo"
}
failover_tool:PRIMARY> db.bar.find().pretty()
{
"_id" : ObjectId("5ce72e0c5267960532b8df06"),
"name" : "bar1",
"foo" : "foo1"
}
{
"_id" : ObjectId("5ce72e165267960532b8df07"),
"name" : "bar2",
"foo" : "foo1"
}
{
"_id" : ObjectId("5ce72e1d5267960532b8df08"),
"name" : "bar3",
"foo" : "foo2"
}
{
"_id" : ObjectId("5ce72e415267960532b8df09"),
"name" : "foo1",
"desc" : "first foo",
"bars" : ["bar1", "bar2"]
},
{
"_id" : ObjectId("5ce72e4a5267960532b8df0a"),
"name" : "foo2",
"desc" : "second foo",
"bars" : ["bar3"]
}
最近的
bars
字段:
db.foo.aggregate({
$lookup: {
from:"bar",
localField:"name",
foreignField: "foo",
as:"bars"
}
}).pretty()