MongoDB使用外键将字段复制到另一个集合 [英] MongoDB copy a field to another collection with a foreign key

问题描述

我想将颜色从用户集合复制到Car集合.我正在使用一个外键，即用户ID.

I want to copy over the color from user collection to the Car collection. I'm using a foreign key which is userID.

> db.test1.User.find()
{ "_id" : ObjectId("515f7db83f71d6bcb1c41a48"), "age" : 33, "Color" : "blue" }
{ "_id" : ObjectId("515f7dc03f71d6bcb1c41a49"), "age" : 52, "Color" : "red" }
{ "_id" : ObjectId("515f7dc43f71d6bcb1c41a4a"), "age" : 43, "Color" : "yellow" }


> db.test2.Car.find()
{ "_id" : ObjectId("515f84883f71d6bcb1c41a54"), "speed" : 291, "userID" : ObjectId("515f7db83f71d6bcb1c41a48") }
{ "_id" : ObjectId("515f84883f71d6bcb1c41a55"), "speed" : 202, "userID" : ObjectId("515f7db83f71d6bcb1c41a49") }
{ "_id" : ObjectId("515f84883f71d6bcb1c41a56"), "speed" : 193, "userID" : ObjectId("515f7db83f71d6bcb1c41a4a") }

这是我的查询

db.test1.User.find().forEach( 
function(x)
{
  db.test2.Car.update( { userID: x._id }, { $set: { color: x.color} } ) 
} );

我想要这个结果:

> db.test2.Car.find()
{ "_id" : ObjectId("515f84883f71d6bcb1c41a54"), "speed" : 291, "userID" : ObjectId("515f7db83f71d6bcb1c41a48"), "color" : "blue" }
{ "_id" : ObjectId("515f84883f71d6bcb1c41a55"), "speed" : 202, "userID" : ObjectId("515f7db83f71d6bcb1c41a49"), "color" : "red" }
{ "_id" : ObjectId("515f84883f71d6bcb1c41a56"), "speed" : 193, "userID" : ObjectId("515f7db83f71d6bcb1c41a4a"), "color" : "yellow" }

感谢您的帮助！

推荐答案

测试设置存在几个问题:

There are several issues with your test set up:

• 字段名称的大小写不匹配(复制时您引用的是color而不是Color)
• 目标集合中只有一个示例外键匹配:ObjectId('515f7db83f71d6bcb1c41a48')
• 您的更新只会影响外键"的第一个匹配文档.对于1:1关系，这是很好的，但对于1:1:1关系，则不是

• Case of field names does not match (you are referencing color instead of Color when copying)
• Only one of the example foreign keys matches in the target collection: ObjectId('515f7db83f71d6bcb1c41a48')
• Your update will only affect the first matching document for the "foreign key". This would be fine for a 1:1 relationship, but not a 1:many

一个纠正了上述问题的示例(除了不匹配的键):

A corrected example taking the above into account (aside from the non-matching keys):

db.test1.User.find().forEach( 
    function(x) {
        db.test2.Car.update(
            // query 
            { userID: x._id },

            // update 
            { $set: { color: x.Color} },

            // options:
            { "multi" : true } // Update all matching documents
        );
    }
);

这将为样本文档中实际匹配的唯一外键设置{color:blue}:

Which results in setting {color:blue} for the only foreign key that actually matches in the sample documents:

db.test2.Car.find()
{
    "_id" : ObjectId("515f84883f71d6bcb1c41a55"),
    "speed" : 202,
    "userID" : ObjectId("515f7db83f71d6bcb1c41a49")
}
{
    "_id" : ObjectId("515f84883f71d6bcb1c41a56"),
    "speed" : 193,
    "userID" : ObjectId("515f7db83f71d6bcb1c41a4a")
}
{
    "_id" : ObjectId("515f84883f71d6bcb1c41a54"),
    "color" : "blue",
    "speed" : 291,
    "userID" : ObjectId("515f7db83f71d6bcb1c41a48")
}

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