How to make composite key in Room

Question

I have just found @PrimaryKey annotation in room. So If I want to make composite key so how can I do that?

Yes CommonsWare these both are independent. Thanks for pointing it out, I'll modify my question. — Lalit Kushwah, Dec 01 '17 at 10:39

score 122 · Accepted Answer · edited Aug 28 '20 at 12:02

122

Make use of primaryKeys().

Android Developer Documentation for Room states:

If PrimaryKey annotation is used on a Embeddedd field, all columns inherited from that embedded field becomes the composite primary key (including its grand children fields).

Example implementation in Java:

@Entity(primaryKeys = {"column1","column2","column3"})
public class DummyClass {
    ...
}

Example implementation in kotlin:

@Entity(primaryKeys = ["column1","column2","column3"])
class DummyClass {
    ...
}

Thanks Lalit Kushwah for the example.

edited Aug 28 '20 at 12:02

Abhinav Atul

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answered Nov 06 '17 at 06:11

Sneh Pandya

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Thanks It worked, Here I am sharing the implementation in case if anyone requires: @Entity (primaryKeys = {"column1","column2"}) – Lalit Kushwah Dec 01 '17 at 10:37
1

Is this the example of creating a composite primary key ?? – K Pradeep Kumar Reddy Jun 01 '20 at 05:58
yes this one is example of creating composite primary key – Anju mohan Nov 29 '22 at 06:08

score 31 · Answer 2 · edited Jul 31 '20 at 20:30

31

Here is an example for Kotlin:

import android.arch.persistence.room.Entity

@Entity(primaryKeys= [ "first_name", "last_name" ] )
class User{
    .......
}

edited Jul 31 '20 at 20:30

Rautermann

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answered May 04 '18 at 13:23

Prakash

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How to make one of them as `autogenerate = true`? – Wahib Ul Haq May 07 '18 at 12:58
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@WahibUlHaq https://stackoverflow.com/questions/46790830/how-to-make-primary-key-auto-increment-while-using-composite-primary-keys-in-roo that might answer your question – Prakash May 15 '18 at 18:43
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Use '{' instead of '[' – Palm Jun 26 '18 at 17:18
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I think for java you need `{` and for kotlin you need `[` – Manohar Jul 19 '18 at 09:55

score 9 · Answer 3 · answered Apr 18 '19 at 04:53

This worked for me I'm using Kotlin 1.3, I think.

@Entity(tableName = "location_table", primaryKeys = ["lat", "lon"])
    data class MyLocation(
    //    @PrimaryKey(autoGenerate = true) var id: Long?,
        var lat: Double,
        var lon: Double,
        var dateTime: String,
        var weatherDescription: String,
        var temperature: Double
    )

score 4 · Answer 4 · answered Dec 19 '19 at 00:38

You can declare an entity on top of your existing entity class such as following

@Entity
 (tableName = "Equipment_History", primaryKeys = {"EquipName","EquipFunctionalLocation"})
public class EquipmentHistory {

    @ColumnInfo @NonNull
    private String EquipFunctionalLocation;
    @ColumnInfo @NonNull
    private String EquipName;
//rest of the columns 

}

In this way you can have the table name of your own choice and also can declare a composite primary key in room but make sure you add the @NonNull annotation alongside your @ColumnInfo annotation otherwise the code won't work, because room will give you a compile-time error otherwise as stated on the google developers website. Hope, this will help.

How to make composite key in Room

4 Answers4

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