MySql Like Auto Increment Numeric Primary Key For Loopback with MongoDB

Using MongoDB’s default ObjectId is a good practice but if you want the MySql like Numeric Auto Increment primary key, then try the steps bellow.

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You can use this method in a specific Model.js file. But here we’ll create a Mixin for that because we’re gonna include this mixin in any Model so that we can have the auto increment feature in Any Model.

For our reference we’ll use a model named customer which extends the default User Model.

STEP 1:

If your Model’s base Model is PersistedModel (not the default User model) then Skip to Step 2 . Now If your model’s base model is User, then you have to make the public attribute of the default User model false in server/model-config.json as bellow.

"User": {
    "dataSource": "mongo",
    "public": false  // We made it public false
  }

STEP 2:

First we’ll create a file named “auto-increment-primary-key.js” in “common/mixins/” (you can create anywhere else you put your mixins) with the bellow content

module.exports = function(Model, options) {
    var modelName = Model.definition.name;     //Get the Model Name from Model Instance
    Model.observe('before save', function (ctx, next) {
        if (!ctx.isNewInstance) {
            next();
        }else{
            Model.getDataSource().connector.connect(function (err, db) {
                var collection = db.collection('counter');
                collection.findAndModify({name: modelName}, [['_id', 'asc']], {$inc: {value: 1}}, { new: true, upsert: true }, function (err, rec) {
                    if (err) {
                        console.err(err);
                        next();
                    } else {
                        getPrimaryKeyFromModel(Model, function(primaryKey){
                            if (ctx.instance) {
                                ctx.instance[primaryKey]   = rec.value.value;
                            } else {
                                ctx.data[primaryKey]  = rec.value.value;
                            }
                            next();
                        });
                    }
            
                });
            });
        }
    });
}
//Get the Primary Key from Model
var getPrimaryKeyFromModel = function(Model,cb){
    var properties = Model.definition.rawProperties;
    Object.keys(properties).forEach(function(key) {
        if(properties[key].id === true){
            cb(key);
        }
    });
}

STEP 3:

Now in our customer.json files disable the “idInjection” as

"idInjection": false

STEP 4:

And in the same customer.json file enable our new Mixin “autoIncrementPrimaryKey” as follows

"mixins": {
    "autoIncrementPrimaryKey": true
  }

STEP 5:

And declare customer_id field as primary key by setting “id” : true as follows

"customer_id": {
      "type": "number",
      "id": true,
      "required": true
    },

So our customer.json will finally look like

{
  "name": "customer",
  "base": "User",
  "idInjection": false,
  "options": {
    "validateUpsert": true
  },
  "mixins": {
    "autoIncrementPrimaryKey": true
  },
  "properties": {
    "customer_id": {
      "type": "number",
      "id": true,
      "required": true
    },
    "customer_name": {
      "type": "string",
      "required": true
    }
  },
  "validations": [],
  "relations": {},
  "acls": [],
  "methods": {}
}

Now create a model instance by the POST method and the id should be generated automatically.

Feel free to comment if you have any suggestions or query.