How to migrate from table without primary key using room?

Question

I'm trying to migrate to room, but the schema of my table was like this:

CREATE TABLE cache(key text, content text, time integer);

Entity:

@Entity(tableName = "cache")
public class Cache{
    public Integer id;
    public String key;
    public String content;
    public Integer time;
}

No primary key was declared explicit, an error would occur while build:

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

I tried to add primary key to the table, but seems sqlite does not support that, anyone could help me?

Answer 1

Excerpt from here: http://www.sqlitetutorial.net/sqlite-primary-key/

Unlike other database systems e.g., MySQL, PostgreSQL, etc., you cannot use the ALTER TABLE statement to add a primary key to an existing table.

To work around this, you need to:

• Set the foreign key check off
• Rename the table to another table name (old_table)
• Create a new table (table) with the exact structure of the table you have been renamed
• Copy data from the old_table to the table
• Turn on the foreign key check on