MongoDB使用外键将字段复制到另一个集合

Question

我想将用户集合中的颜色复制到Car集合中.我使用的是外键,即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" }

谢谢你的帮助 !

Answer 1

您的测试设置存在几个问题：

• 字段名称大小写不匹配（要引用color而不是Color复制时）
• 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，这很好，但对于1：1：1而言，不是

纠正了上述问题的示例（除了不匹配的键）：

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
        );
    }
);

这样就可以设置{color:blue}样本文档中实际匹配的唯一外键：

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")
}