how to pass different values to a variable in a scala object

Question

I want to create different collection in mongodb for that i have a scala object class here is my code

object Factory {

val connectionMongo = MongoConnection(SERVER)
val collectionMongo = connectionMongo(DATABASE)("collectionA")

}

i want to add different collection names for that i am doing it like this object class here is my code

    object Factory {

    var COLLECTIONName:String=""
    def setCollectionName(name:String)
    {
      COLLECTIONName=name
    }
    val connectionMongo = MongoConnection(SERVER)
    val collectionMongo = connectionMongo(DATABASE)(COLLECTIONName)

    }

class testA {

//getting collection object 
Factory.setCollectionName("collectionA")
collectionMongo.find()//fetching the record of collectionA

}

class testB {

//getting collection object 
Factory.setCollectionName("collectionB")
collectionMongo.find()//fetching the record of collectionB
}

but this code is not working as desired it always gets COLLECTIONName value to empty string "" please guide me where i am doing wrong ,please help

can you explain it via example i am having difficulty in understanding — sarah w
– sarah w, Commented Jun 24, 2016 at 6:35

LynxZh · Accepted Answer · 2016-06-24 08:18:53Z

1

This is a typical factory pattern, you can change your collectionMongo from a val into a function like this

object Factory {
    val SERVER = "<some server>"
    val DATABASE = "<some database>"
    val connectionMongo = MongoConnection(SERVER)(DATABASE)
    def getCollection(name: String) = connectionMongo(name)
}

Usage

class testA {
    val collectionA = Factory.getCollection(nameA)
}

class testB {
    val collectionB = Factory.getCollection(nameB)
}

answered Jun 24, 2016 at 8:18

LynxZh

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Comments

Shivansh · Accepted Answer · 2016-06-24 06:47:44Z

1

you have written

val COLLECTIONName:String=""

And then you are reassigning the value. You cannot reassign a value in val, instead of it use var. But that's a bad approach too.. So try to modify the code so that it must be written in a more functional way.

The modified code would be something like :

class Factory(connectionName:String) {
    val connectionMongo = MongoConnection(SERVER)
    val collectionMongo = connectionMongo(DATABASE)(connectionName)
}

class testA {
    //getting collection object 
    val factory=new Factory("collectionA")
    factory1.collectionMongo.find()//fetching the record of collectionA
}

class testB {
    //getting collection object 
    val factory=new Factory("collectionB")
    factory.collectionMongo.find()//fetching the record of collectionB
}

I am not sure if this is the best way but its totally a better way.

The singleton object Approach as asked:

object Factory {
    var connectionName:String=_
    val connectionMongo = MongoConnection(SERVER)
    def collectionMongo = connectionMongo(DATABASE)(connectionName)

    }

class testA {

//getting collection object 
 Factory.connectionName="collectionA"
Factory.collectionMongo.find()//fetching the record of collectionA

}

class testB {

//getting collection object 
 Factory.connectionName="collectionB"
Factory.collectionMongo.find()//fetching the record of collectionB
}

I hope that helps !

edited Jun 24, 2016 at 6:47

answered Jun 24, 2016 at 6:26

Shivansh

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4 Comments

sarah w Over a year ago

sorry its a typo i have edited it ,its actually var ...can you please explain a better approach with an example ?

Shivansh Over a year ago

I have updated the answer take a look ! :) And upvote ! :D

sarah w Over a year ago

thanks but i want to use scala object because i need a singleton object ,thats why i am not using scala class

Shivansh Over a year ago

But using var and overiding the values is a bad approach AFAIK, and if you want to follow the singleton object approach then use var there, and check the updated code.

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