首页 \ 问答 \ 如何在MongoDB中返回文档的ObjectId或_id？(How to return the ObjectId or _id of an document in MongoDB? and error “$in needs an array”)

如何在MongoDB中返回文档的ObjectId或_id？(How to return the ObjectId or _id of an document in MongoDB? and error “$in needs an array”)

 我在MongoDB中有一个文档，我想得到这个文档的ObjectId，但到目前为止我还没有找到一个对我这样做的方法。  
 查询示例：  
 user= db.users.find({userName:"Andressa"})
 
 这返回：  
 { "_id" : ObjectId("53b1c579bdf3de74f76bdac9"), "userid" : 0, "userName" : "Andressa", "userEmail" : "dessa_beca@hotmail.com", "teams" : [ 1, 2, 3 ] }
 
 我想让ObjectId做另一个查询。  
 例：  
 userID =  `user._id();` //but this does not work, of course, its an example
 
 所以，我可以使用ObjectId来执行另一个查询，如下所示：  
 userFind = db.users.find({_id: userID})
 
 更新：此代码：  
 db.teams.find({_id:{$in: user.teams}})
 
 返回此错误：  
error: {
    "$err" : "Can't canonicalize query: BadValue $in needs an array",
    "code" : 17287
 
 有人知道吗？ 

I have a document in MongoDB and I would like to get the ObjectId of this document, but I did not find so far a method that does this to me.  
Example of query : 
 user= db.users.find({userName:"Andressa"})
 
This returns this : 
 { "_id" : ObjectId("53b1c579bdf3de74f76bdac9"), "userid" : 0, "userName" : "Andressa", "userEmail" : "dessa_beca@hotmail.com", "teams" : [ 1, 2, 3 ] }
 
I want get the ObjectId to do another query .  
Example: 
 userID =  `user._id();` //but this does not work, of course, its an example
 
So, I could user the ObjectId to do another query like this: 
 userFind = db.users.find({_id: userID})
 
UPDATE: This code : 
 db.teams.find({_id:{$in: user.teams}})
 
returns this error:  
error: {
    "$err" : "Can't canonicalize query: BadValue $in needs an array",
    "code" : 17287
 
Does someone know it? 

原文：https://stackoverflow.com/questions/24557580

更新时间：2024-02-17 18:02

最满意答案

 只需删除此：  
        //Make sure entity knows EquipmentOwned has been modified
        db.Entry(ninja.EquipmentOwned).State = EntityState.Modified;
 
 这会导致错误。  
 EquipmentOwned是List<Equipment> 。 它不是EF Entry ，因此不会直接跟踪它。  
 当您从此类集合中删除实体时， EF知道此特定忍者与此特定设备之间不存在任何关系。 它不会从数据库中删除设备，因为其他忍者可能会使用此设备。  
 要完全删除它，您应该从相应的DbSet<>删除此设备，如下所示：  
using (var db = new NinjaContext())
{
    //db.Equipment is a DbSet<Equipment>
    //id is PrimaryKey of Equipment table
    var eq = db.Equipment.Find(id);
    db.Equipment.Remove(eq);
    db.SaveChanges();
}

Just remove this: 
        //Make sure entity knows EquipmentOwned has been modified
        db.Entry(ninja.EquipmentOwned).State = EntityState.Modified;
 
This causes the error. 
EquipmentOwned is a List<Equipment>. It is not an Entry in EF terms so it is not tracked directly by it. 
When you delete an entity from such collection, EF knows that there won't be any relationship between this particular ninja and this particular equipment. It won't delete equipment from database because other ninjas may use this equipment. 
To delete it completely you should remove this equipment from corresponding DbSet<> like this: 
using (var db = new NinjaContext())
{
    //db.Equipment is a DbSet<Equipment>
    //id is PrimaryKey of Equipment table
    var eq = db.Equipment.Find(id);
    db.Equipment.Remove(eq);
    db.SaveChanges();
}

如何在MongoDB中返回文档的ObjectId或_id？(How to return the ObjectId or _id of an document in MongoDB? and error “$in needs an array”)

最满意答案

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