EDITED TO INCLUDE CORRECT SOLUTION

这正是我学习Mongo的问题 - 你正在寻找与 update 命令一起使用的 $addToSet 运算符(see docs here)，以及你正在使用的 $ 位置运算符 .

$ addToSet {$ addToSet：{field：value}}仅当数组不在数组中时才向数组添加值 .

因此查询变为(db.stack是我用于测试目的的集合)，示例运行如下：

db.stack.update({ "trips.name":"2010-05-10" },

{ $addToSet: { "trips.$.loc":{"lat":11, "lng":12} } }

);

TEST RUN(带有一些不重要元素空间的缩写)：

#### YOUR ITEM IN THE DB

> db.stack.find({"trips.name":"2010-05-10"})

{ "_id" : ObjectId("4c28f62cbf8544c60506f11d"), "some_other_data" : "goes here",

"trips" : [

{ "name" : "2010-05-10",

"loc" : [ {

"lat" : 21.321231,

"lng" : 16.8783234,

"updated_at" : "Mon May 10 2010 15:24:35"

}, { "lat" : 21.321231,

"lng" : 16.8783234,

"updated_at" : "Mon May 10 2010 15:24:24"

} ] },

{ "name" : "2010-05-08",

"loc" : [ ... ]

} ] }

#### SUCCESSFULLY ADDS ITEM TO PROPER ARRAY

> db.stack.update({"trips.name":"2010-05-10"}, {$addToSet: {"trips.$.loc":{"lat":11, "lng":11}}});

> db.stack.findOne()

{ "_id" : ObjectId("4c28f62cbf8544c60506f11d"), "some_other_data" : "goes here",

"trips" : [

{ "loc" : [

{ "lat" : 21.321231,

"lng" : 16.8783234,

"updated_at" : "Mon May 10 2010 15:24:35"

}, { "lat" : 21.321231,

"lng" : 16.8783234,

"updated_at" : "Mon May 10 2010 15:24:24"

}, { "lat" : 11,

"lng" : 11

}

], "name" : "2010-05-10"

},

{ "name" : "2010-05-08",

"loc" : [ ... ]

} ] }

#### ON REPEAT RUN DOESN'T ADD NEW ELEMENT

> db.stack.update({"trips.name":"2010-05-10"}, {$addToSet: {"trips.$.loc":{"lat":11, "lng":11}}});

> db.stack.findOne()

{ "_id" : ObjectId("4c28f62cbf8544c60506f11d"), "some_other_data" : "goes here",

"trips" : [ {

"loc" : [

{ "lat" : 21.321231,

"lng" : 16.8783234,

"updated_at" : "Mon May 10 2010 15:24:35"

}, { "lat" : 21.321231,

"lng" : 16.8783234,

"updated_at" : "Mon May 10 2010 15:24:24"

}, { "lat" : 11,

"lng" : 11

}

], "name" : "2010-05-10"

},

{ "name" : "2010-05-08",

"loc" : [ ... ]

} ] }

#### BUT WILL CORRECTLY ADD ANOTHER ELEMENT TO THE SAME ARRAY IF IT'S NOT PRESENT

> db.stack.update({"trips.name":"2010-05-10"}, {$addToSet: {"trips.$.loc":{"lat":11, "lng":12}}});

> db.stack.findOne()

{ "_id" : ObjectId("4c28f62cbf8544c60506f11d"), "some_other_data" : "goes here",

"trips" : [

{ "loc" : [

{ "lat" : 21.321231,

"lng" : 16.8783234,

"updated_at" : "Mon May 10 2010 15:24:35"

}, { "lat" : 21.321231,

"lng" : 16.8783234,

"updated_at" : "Mon May 10 2010 15:24:24"

}, { "lat" : 11,

"lng" : 11

}, { "lat" : 11,

"lng" : 12

}

], "name" : "2010-05-10"

},

{ "name" : "2010-05-08",

"loc" : [ ... ]

} ] }