TA貢獻(xiàn)1827條經(jīng)驗 獲得超8個贊
可以使用別名,不過要用
aggregate()進(jìn)行查詢,并且,要把需要顯示的名稱全部列出來
你要將需要顯示的列,全部寫在
$project中
db.getCollection('discerns').aggregate([
{
$project: {
'date': '$DateTime'
}
}
]);如果要起別名,對象的鍵就是別名,值就是實際的數(shù)據(jù)庫字段名(字段名要用$符號開頭,否則 mongodb 會將其解析為一個字符串)
_id會默認(rèn)查詢出來,如果不想要 _id 查詢出來,需要手動設(shè)置 _id:0
除 _id外,其他字段值不設(shè)置,則不會查詢出來
TA貢獻(xiàn)1946條經(jīng)驗 獲得超3個贊
可以的，將投射過的字段在結(jié)果中重命名：
原始數(shù)據(jù)：
> db.zipcode.find()
{ "_id" : "01001", "city" : "AGAWAM", "loc" : [ -72.622739, 42.070206 ], "pop" : 15338, "state" : "MA" }
{ "_id" : "01002", "city" : "AGAWAM", "loc" : [ -72.51565, 42.377017 ], "pop" : 36963, "state" : "MA" }
{ "_id" : "01005", "city" : "AGAWAM", "loc" : [ -72.108354, 42.409698 ], "pop" : 4546, "state" : "MA" }
{ "_id" : "01007", "city" : "BELCHERTOWN", "loc" : [ -72.410953, 42.275103 ], "pop" : 10579, "state" : "MA" }
{ "_id" : "01008", "city" : "BLANDFORD", "loc" : [ -72.936114, 42.182949 ], "pop" : 1240, "state" : "MA" }
顯示原字段和重命名字段名稱：
> db.zipcode.aggregate({$project:{myid:"$_id"}})
{ "_id" : "01001", "myid" : "01001" }
{ "_id" : "01002", "myid" : "01002" }
{ "_id" : "01005", "myid" : "01005" }
{ "_id" : "01007", "myid" : "01007" }
{ "_id" : "01008", "myid" : "01008" }
只顯示重命名字段名稱：
> db.zipcode.aggregate({$project:{myid:"$_id",_id:0}})
{ "myid" : "01001" }
{ "myid" : "01002" }
{ "myid" : "01005" }
{ "myid" : "01007" }
{ "myid" : "01008" }
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