MongoDB中查询数组以获取特定值
要从数组中获取特定值，请使用aggregate()和$project。让我们创建一个包含文档的集合-
> db.demo761.insertOne(
... {
... "details": [
... {
... "student": {
... "FullName": "Chris Brown"
... }
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eb034d15637cd592b2a4af1")
}
> db.demo761.insertOne(
... {
... "details": [
... {
... "student": {
... "FullName": "Chris Taylor"
... }
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eb034d25637cd592b2a4af2")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo761.find();
这将产生以下输出-
{ "_id" : ObjectId("5eb034d15637cd592b2a4af1"), "details" : [ { "student" : { "FullName" : "Chris Brown" } } ] }
{ "_id" : ObjectId("5eb034d25637cd592b2a4af2"), "details" : [ { "student" : { "FullName" : "Chris Taylor" } } ] }以下是如何在MongoDB中查询数组-
> db.demo761.aggregate([
... {'$unwind':'$details'},
... {'$match': {
... 'details.student.FullName':'Chris Taylor',
... }},
... {'$project': {
... 'details.student.FullName': 1, '_id': 0
... }},
... ])这将产生以下输出-
{ "details" : { "student" : { "FullName" : "Chris Taylor" } } }