How to annotate a default value inside a android room entity?

Question

I couldn\'t find any information how to annotate a SQL - \"DEFAULT\" value while looking into the @ColumnInfo docs for the new Android Persistence Library.

Does Room

Answer 1

For any one facing the situation when you have two foreign keys and "onDelete = CASCADE" you can set the foreign key to a data type that can be set to null for example:

int parent1Id = 0;
int parent2Id = 0;  
//should be:
Long parent1Id = null;
Long parent2Id = null;

that way the DB knows that a particular Object/row has no other parent of different type when attempting to delete it when its parent is deleted.

Answer 2

You can check inside your getter method of Entity and set some default value there.

@Entity(tableName = "Dashboard")
public class Dashboard {
@PrimaryKey
@NonNull
@ColumnInfo(name = "claimNumber")
private String claimNumber;
private String percentage = "0";
private String imagePath = "";

@NonNull
public String getClaimNumber() {
    return claimNumber;
}

public void setClaimNumber(@NonNull String claimNumber) {
    this.claimNumber = claimNumber;
}



public String getPercentage() {
    if (percentage == null || percentage.isEmpty()) {
        return "0";
    }
    return percentage;
}

public void setPercentage(String percentage) {
    this.percentage = percentage;
}

public String getImagePath() {
    return imagePath;
}

public void setImagePath(String imagePath) {
    this.imagePath = imagePath;
}

public Dashboard(@NonNull String claimNumber,  String percentage, String imagePath) {
    this.claimNumber = claimNumber;

    this.percentage = percentage;
    this.imagePath = imagePath;
}

}

Answer 3

Room hasn't any annotation for default value, but you can set default value in your entity like this:

@Entity(tableName = "MyTable")
class MyClass {
    ...

    public String MyDefaultValuedCol = "defaultString";

    public boolean MyDefaultFlagCol = true;

}

Answer 4

You can set the default value using @ColumnInfo annotation-

@ColumnInfo(defaultValue = "No name")
public String name;

and

@ColumnInfo(defaultValue = "0")
public int flag;

or for any kind of data types check the reference from here Google developer doc

Answer 5

With the release of room persistence 2.2.0, there's a new property added to @ColumnInfo annotation which can be used to specify the default value of a column. See documentation.

@Entity(tableName = "users")
data class User(
    @PrimaryKey val id: Long,
    @ColumnInfo(name = "user_name", defaultValue = "temp") val name: String
    @ColumnInfo(name = "last_modified", defaultValue = "CURRENT_TIMESTAMP" ) val lastModified: String
)