Home / Questions / 250530
Accepted
cosito
Asked: 2020-04-01 22:36:20 +0800 CST 2020-04-01 22:36:20 +0800 CST

over writing to mongo's default _id

  • 772

I have this collectionin mongo, but my question is is there any way that when doing one collectionwith insertno I get the _iddefault since this time I use my idas the second line.

{
        "_id" : ObjectId("5ca1abb6ce037511f000628e"),
        "id" : "sjohnson",
        "name" : "Steve Johnson"
}

I need it to be like this:

   {
            "id" : "sjohnson",
            "name" : "Steve Johnson"
    }
mongodb

2 Answers

  1. Best Answer

    According to the official documentation if your collection doesn't have a column _idexplicitly; then MongoDB will create a column _idand write a hexadecimal value of type ObjectId.

    If you are going to handle the column with your own values, _idthen you only have to make sure that said column receives unique values ​​that are provided by yourself.

    EXAMPLE 1

    Let's create an example database like this

    use mydb

    Later, we execute the following command to insert a value into a users collection

    db.users.insert({ "_id": 1, "name": "alfa" })

    If we execute a find()to said collection it will return this

    db.users.find()

    Result

    {"_id": 1, "name": "alpha"}

    With the above you have been able to verify that if you explicitly declare a column _id, it will be respected and mongoDB will not add one by default

    EXAMPLE 2

    Now we are going to insert a new record, but this time we will omit the column _idwhich will give way to the mongoDB manager to add the column by itself assigning a default value

    db.users.insert({ "name": "beta", "age": 28 })

    If I now run the following command

    db.users.find()

    I will get the following as a result

    { "_id": ObjectId("5ca1b6a90193271048449020"), "name": "beta", "age": 28 }

    • 2

  2. The _idMongoDB field must be present in every document that is stored in the database. If a document does not have such a field at the time of performing a insert, MongoDB will create that field for us.

    Therefore we cannot get rid of said field. That is, you cannot remove it from your documents.

    In your question, you state that you want to use your own field id. You have 2 options:

    1. You can override the field _idby sending the value for that field in your document. However, you must be able to guarantee that such a field is unique. Perhaps sjohnsonit is not the most appropriate. If a user is called Steve Johnsonand you generate the _idtaking the initial of the name and the last name, then, Sam Johnsonfor example, it is already a name that you will not be able to store with this procedure. In many places the identity document number is used as a field _idsince a unique relationship is assumed. In other cases, email is used. An integerautoincrement type value is also used. You already have something to pull from there. Just remember that when you insert your document, it must have a field _idwith a value that is unique to that document.

    2. You can ignore the fact that such a field exists, and skip it when making your query. You can also create your own field id, just as you currently do, and use the same value for both id, _idalways keeping in mind what I mentioned in the previous point.

    An example could be the following:

    > db.users.insert({"_id": "Y12345678W", "id": "Y12345678W", "name": "Steve", "lastname": "Johnson"})

    At the time of making the query, I can tell Mongo to skip bringing me the field, _idfor example with the following query find:

    > db.users.find({}, {"_id": 0})
{"id": "Y12345678W", "name": "Steve", "lastname": "Johnson"}

    As you can see, in the query I have passed as the second argument a document called parameterprojection , which specifies the fields that I want the query to return. A value of 0( false) indicates that the field will not be returned, and a value of 1( true) indicates that it will be returned.

    When the parameter is omitted projection, MongoDB returns all fields in the document. On the other hand, if a parameter is passed projectionindicating one (or some) value in false, the rest is assumed true, except for the field _idthat is always assumed true. That is what happens in the query that we just made.

    On the other hand, if we pass a parameter projection, indicating one (or some) values ​​in true, the rest are assumed to be false(except the field _id) and are not returned by the query.

    For example, if we want only the field idand the field, lastnamewe can perform the following query:

    >db.users.find({}, {"_id": 0, "id": 1, "lastname": 1})
{"id": "Y12345678W", "lastname": "Johnson"}

    Finally, note that the only field that MongoDB uses as PKis the field _id, this means that no other field can be set as Primary Key.

    In addition, MongoDB allows you to establish any other field such as unique index, (understand that not Primary Key) that must meet the necessary conditions to be considered a unique type index.

    I hope this clears your doubt.

    • 1