给定此文档保存在MongoDB中
{
_id : ...,
some_key: {
param1 : "val1",
param2 : "val2",
param3 : "val3"
}
}
需要保存具有来自外部世界的关于param2和param3的新信息的对象
var new_info = {
param2 : "val2_new",
param3 : "val3_new"
};
我想在对象的现有状态上合并/覆盖新字段,这样param1就不会被删除
这样做
db.collection.update( { _id:...} , { $set: { some_key : new_info } }
将导致MongoDB完全按照要求执行,并将some_key设置为该值。更换旧的。
{
_id : ...,
some_key: {
param2 : "val2_new",
param3 : "val3_new"
}
}
如何让MongoDB只更新新字段(而不显式地逐个声明它们)?要得到这个:
{
_id : ...,
some_key: {
param1 : "val1",
param2 : "val2_new",
param3 : "val3_new"
}
}
我正在使用Java客户端,但是任何示例都将受到欢迎
您可以使用点符号来访问和设置对象内部深处的字段,而不会影响这些对象的其他属性。
给定你上面指定的对象:
> db.test.insert({"id": "test_object", "some_key": {"param1": "val1", "param2": "val2", "param3": "val3"}})
WriteResult({ "nInserted" : 1 })
我们可以只更新some_key。Param2和some_key.param3:
> db.test.findAndModify({
... query: {"id": "test_object"},
... update: {"$set": {"some_key.param2": "val2_new", "some_key.param3": "val3_new"}},
... new: true
... })
{
"_id" : ObjectId("56476e04e5f19d86ece5b81d"),
"id" : "test_object",
"some_key" : {
"param1" : "val1",
"param2" : "val2_new",
"param3" : "val3_new"
}
}
你想挖多深就挖多深。这对于在不影响现有属性的情况下向对象添加新属性也很有用。
从Mongo 4.2开始,db.collection.updateMany()(或db.collection.update())可以接受一个聚合管道,它允许使用聚合操作符,如$addFields,它输出输入文档中所有现有的字段和新添加的字段:
var new_info = { param2: "val2_new", param3: "val3_new" }
// { some_key: { param1: "val1", param2: "val2", param3: "val3" } }
// { some_key: { param1: "val1", param2: "val2" } }
db.collection.updateMany({}, [{ $addFields: { some_key: new_info } }])
// { some_key: { param1: "val1", param2: "val2_new", param3: "val3_new" } }
// { some_key: { param1: "val1", param2: "val2_new", param3: "val3_new" } }
The first part {} is the match query, filtering which documents to update (in this case all documents).
The second part [{ $addFields: { some_key: new_info } }] is the update aggregation pipeline:
Note the squared brackets signifying the use of an aggregation pipeline.
Since this is an aggregation pipeline, we can use $addFields.
$addFields performs exactly what you need: updating the object so that the new object will overlay / merge with the existing one:
In this case, { param2: "val2_new", param3: "val3_new" } will be merged into the existing some_key by keeping param1 untouched and either add or replace both param2 and param3.