从 sqlite 到房间的数据库迁移预期表处理

Question

I keep getting this error and I still don't know how to solve it. Please help me out here. This are my error Logs :

java.lang.RuntimeException: Exception while computing database live data.

 Caused by: java.lang.IllegalStateException: Migration didn't properly handle: task(com.examples.TaskEntry).

 Expected:
    TableInfo{name='task', columns={description=Column{name='description', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, id=Column{name='id', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}, priority=Column{name='priority', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, updated_at=Column{name='updated_at', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[], indices=[]}


Found:
    TableInfo{name='task', columns={}, foreignKeys=[], indices=[]}

Below is my TaskEntry Entity Class where I presume all the problem originates from:

@Entity(tableName = "task")
public class TaskEntry {

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "description")
    @NonNull
    private String description;

    @ColumnInfo(name = "priority")
    private int priority;

    @ColumnInfo(name = "updated_at")
    private Date updatedAt;

    @Ignore
    public TaskEntry(@NonNull String description, int priority, Date updatedAt) {
        this.description = description;
        this.priority = priority;
        this.updatedAt = updatedAt;
    }

    public TaskEntry(int id, @NonNull String description, int priority, Date updatedAt) {
        this.id = id;
        this.description = description;
        this.priority = priority;
        this.updatedAt = updatedAt;
    }

In this code I manage to call the Migration instance to my Room Database Class:

final static Migration MIGRATION_5_6 = new Migration(5, 6) {
    @Override
    public void migrate(@NonNull SupportSQLiteDatabase database) {
        // Since we didn't alter the table, there's nothing else to do here.


    }
};

public static AppDatabase getInstance(Context context) {
    if (sInstance == null) {
        synchronized (LOCK) {
            Log.d(LOG_TAG, "Creating new database instance");
            sInstance = Room.databaseBuilder(context.getApplicationContext(),
                    AppDatabase.class, AppDatabase.DATABASE_NAME)
                    .addMigrations(MIGRATION_5_6)
                    .addCallback(roomCallback)


                    .build();
        }
    }
    Log.d(LOG_TAG, "Getting the database instance");

Answer 1

In short, Room has found a database that has no task table, hence there being no columns, foreign keys or indicies.

Below is my TaskEntry Entity Class where I presume all the problem originates from:

This would only be the issue, I beleive, if the table name in the database is not task eg if the table were named tasks and @Entity(tableName = "task") were used instead of @Entity(tableName = "tasks")`

Otherwise the issue would appear to perhaps be in the Migration. Perhaps by saying / Since we didn't alter the table, there's nothing else to do here. What is actually happening is that you are introducing the table (otherwsie if not adding or introducing the table why would there be a migration). If that were the case then the Migration should be :-

final static Migration MIGRATION_5_6 = new Migration(5, 6) {
    @Override
    public void migrate(@NonNull SupportSQLiteDatabase database) {
        // Since we didn't alter the table, there's nothing else to do here.
        _db.execSQL("CREATE TABLE IF NOT EXISTS `task` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `description` TEXT NOT NULL, `priority` INTEGER NOT NULL, `updated_at` TEXT)");
    }
};

• Note the SQL has been copied from the createAllTables method in the AppDatabase_Impl.java in the generated Java after compiling (but not running the App).

However, you would likely then get an error :-

error: Cannot figure out how to save this field into database. You can consider adding a type converter for it.

So you would need to eitherr change the updateAt column to be a type of String or Write and Implement a TypeConverter.