How to add primary key in room database?

Question

I have a sqlite database and i want to change my database to Room database.

One of tables has no any primary key and just have two foreign key.

I created the table before room with this query:

CREATE TABLE student_performance(
class_id int , 
student_id char(10), 
class_date date , 
absent boolean DEFAULT 0, 
delay boolean DEFAULT 0, 
positive int DEFAULT 0, 
negative int DEFAULT 0, 
quiz float ,
FOREIGN KEY (student_id , class_id) REFERENCES student(student_id , class_id) 
ON DELETE CASCADE 
ON UPDATE CASCADE);

Now i define table for room:

@Entity(tableName = "performance",
    foreignKeys = {@ForeignKey(
            entity = StudentEntry.class,
            parentColumns = {CLASS_ID, STUDENT_ID},
            childColumns = {CLASS_ID, STUDENT_ID},
            onDelete = CASCADE, onUpdate = CASCADE)})
public class PerformanceEntry {
    .
    .
    .
}

But it gives error :

error: An entity must have at least 1 field annotated with @PrimaryKey

I dont know how can define this table for room database.

Martin Zeitler · Accepted Answer · 2019-08-11T07:59:14.683

6

One does not have to run CREATE TABLE SQL, when having tableName and @ColumnInfo annotations present. Add a primary key entry_id (since the class_id barely is unique):

@Entity(
    tableName = "performance",
    foreignKeys = {
        @ForeignKey(
            entity = StudentEntry.class,
            parentColumns = {CLASS_ID, STUDENT_ID},
            childColumns = {CLASS_ID, STUDENT_ID},
            onDelete = CASCADE,
            onUpdate = CASCADE
       )
   }
)
public class PerformanceEntry  {

    /* Fields */
    @ColumnInfo(name = "entry_id")
    @PrimaryKey(autoGenerate = true)
    private int entryId;

    ...
}

edited Aug 11 '19 at 07:59

answered Aug 11 '19 at 07:53

Martin Zeitler

1
19
155
216

Thank you . I understand what you mean now , If i dont mistake , Either way Room needs a primary key for each table to add, update, and delete operations – Nima Khalili Aug 11 '19 at 11:46

score 1 · Answer 2 · edited Aug 11 '19 at 08:20

1

Example:

primaryKeys = {"class_id", "lastName", "class_date", ... , "quiz"})

In Relational Databases when you don't have any primary key means all of the fields are primary key together.

When you use ORM you should usually define an Id attribute for your entities.

edited Aug 11 '19 at 08:20

Gaurav Mall

2,372
1
17
33

answered Aug 11 '19 at 07:51

taha

731
2
7
18

score 1 · Answer 3 · answered Aug 11 '19 at 07:57

Check the official doc.

Just use the @PrimaryKey annotation.

Each entity must define at least 1 field as a primary key. Even when there is only 1 field, you still need to annotate the field with the @PrimaryKey annotation. Also, if you want Room to assign automatic IDs to entities, you can set the @PrimaryKey's autoGenerate property. If the entity has a composite primary key, you can use the primaryKeys property of the @Entity annotation, as shown in the following code snippet:

Something like:

@Entity(...)
public class PerformanceEntry {
    @PrimaryKey
    public int class_id;

    //..

}

or

@Entity(...)
public class PerformanceEntry {
    @PrimaryKey(autoGenerate = true)

    //..

}

score 0 · Answer 4 · answered Aug 11 '19 at 08:01

0

You need to use the autoGenerate property

Your annotation should be like this:

@PrimaryKey(autoGenerate = true)

answered Aug 11 '19 at 08:01

Aashutosh Poudel

110
1
9

How to add primary key in room database?

4 Answers4