How to ignore some columns during inserting date

Question

When you use Android Room auto generated insert method, it pass all values to all columns For example, if you have an entity like below:

@Entity
public class Task {

    @PrimaryKey(autoGenerate = true)
    public long id;

    @NonNull
    @ColumnInfo(defaultValue = "Unknown Title")
    public String name;

    @NonNull
    @ColumnInfo(defaultValue = "Does not have any description!")
    public String desc;

    @ColumnInfo(defaultValue = "false")
    public boolean isDone;
}

And you try to insert an empty instance of Task class by:

taskDao.insert(new Task());

It will run a query like this:

INSERT INTO Task (id, name, desc, isDone) values (null, null, null, 0);

that is against of our table structure rules, so we get error:

Caused by: android.database.sqlite.SQLiteConstraintException: NOT NULL constraint failed: task.name (code 1299 SQLITE_CONSTRAINT_NOTNULL)

While if it use this query:

INSERT INTO Task DEFAULT VALUES;

or

INSERT INTO Task (id) VALUES (null);

SQLite creates a row with all default values, without any errors.

But to ignore null variables in the insert query for using default valuse?

I will use the default values but with room it passes null to database, instead of ignoring it — golkarm, Mar 10 '21 at 11:31
i don't get what u mean but if u remove the default value from **ColoumnInfo** and pass your default value as a value for the attribute then room will set this default value if the user miss any value u want. — Sami Shorman, Mar 10 '21 at 11:46
You right but what you said sets a value that will passed to database, but value of default column in ColumnInfo will use when where are not a passed value like this query `INSERT INTO TABLE task (name) values ("my task");` that ignores id, description and is_done columns — golkarm, Mar 10 '21 at 11:57

Sam Chen · Answer 1 · 2021-03-10T14:07:39.020

0

Try this:

@Entity
public class Task {
    public String mName = "Unknown Title";
    public String mDescription = "Does not have any description!";
    public boolean mIsDone  = "false";

    @PrimaryKey(autoGenerate = true)    //must be placed at the end!!
    public long id = 0;
}

And create object like this:

Task task = new Task()    //all use default values

Task task = new Task(name)    //use default values for other fileds

Task task = new Task(name, description)    //the order matters, otherwise you need to explicitlty specify the filed, like following

Task task = new Task(mIsDone = true, mName = "Sam")

Room "deaultValue" is not for entity use: https://developer.android.com/reference/androidx/room/ColumnInfo#defaultValue()

edited Mar 10 '21 at 14:07

answered Mar 10 '21 at 14:00

Sam Chen

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why id must be placed at the end?? – golkarm Mar 10 '21 at 15:03
@Mohammad7G https://stackoverflow.com/questions/64517656/android-room-database-create-entity-object-without-id – Sam Chen Mar 10 '21 at 15:16
@Mohammad7G Does it help? – Sam Chen Mar 11 '21 at 03:44
about of 1st part of your answer, pay attention to my question, I explained that it passes null. and in part 2 seems that Room doesn't handle my ask directly – golkarm Mar 11 '21 at 05:50
@Mohammad7G You got null because you didn't give the default value to that field man, `columnInfo(defaultValue)` does not work the way you expect, it's for migration use: https://developer.android.com/training/data-storage/room/migrating-db-versions#handle-default-values-migrations. Just give it a try. – Sam Chen Mar 11 '21 at 11:49

golkarm · Accepted Answer · 2021-03-12T11:54:35.253

Based on what is written in the Android documentation:

The default value you specify here will NOT be used if you simply insert the Entity with @Insert.

That means there are no simple way but you can do it in some ways:

Assign Variables Values

Assign what you defined as default values in @ColumnInfo, for those variables value, because if you doesn't update those values, the default assignment will be used, as Documentation says:

If you simply insert the Entity with @Insert ... any value assigned in Java/Kotlin will be used.

@Entity
public class Task {

    @PrimaryKey(autoGenerate = true)
    public long id;

    @NonNull
    @ColumnInfo(defaultValue = "Unknown Title")
    public String name = "Unknown Title";

    @NonNull
    @ColumnInfo(defaultValue = "Does not have any description!")
    public String description = "Does not have any description!";

    @ColumnInfo(defaultValue = "false")
    public boolean isDone; // it doesn't need assignment
                           // boolean values are false as default
}

Special Query

As Documentation recommend:

Use @Query with an INSERT statement and skip this column there in order to use this default value.

@Query("INSERT INTO task DEFAULT VALUES")
long insert();

or

@Query("INSERT INTO task (id) VALUES (null)")
long insert();

As you told in your question.

Simplified Class (ref)

@Insert(entity = Task.class)
long insert(NewTask task);

@Entity
class NewTask {
    int id = 0;
}

it runs

INSERT INTO task (id) VALUES (null);

How to ignore some columns during inserting date

2 Answers2