Search query using Android room relation

问题

In Android room relation, is it possible to use search query using the property of the related table. Below is my table structure. In this i am relating transaction with payment and lines(transaction items). I have an search field in my UI where the user could search using payment amount which is inside payment table. How to form a query to access the properties of payment table.

class TransactionWithPaymentAndLines(
    @Embedded
    var transactions: Transactions? = null,

    @Relation(
        parentColumn = "id",
        entityColumn = "transactionId",
        entity = Payment::class
    )
    var payments: List<Payment> = listOf(),

    @Relation(
        parentColumn = "id",
        entityColumn = "transactionId",
        entity = TransactionLines::class
    )
    var transactionLines: List<TransactionLines> = listOf()
)

回答1:

Ideal way is to query multiple related tables is to create a View. A view combines data from two or more tables using join.

In Android, using Room Persistance library, you can create such a view, and then you can query the fields of view. This is how you can do it:

Suppose, you have tables:

User: id, name, departmentId

Department: id, name

Create a View:

@DatabaseView("SELECT user.id, user.name, user.departmentId," +
        "department.name AS departmentName FROM user " +
        "INNER JOIN department ON user.departmentId = department.id")
data class UserDetail(
    val id: Long,
    val name: String?,
    val departmentId: Long,
    val departmentName: String?
)

Add View to Database:

@Database(entities = arrayOf(User::class),
          views = arrayOf(UserDetail::class), version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun userDetailDao(): UserDetailDao
}

Create a DAO:

@Dao
interface UserDetailDao {
    @Query("SELECT * FROM UserDetail")
    fun loadAllUserDetails(): Array<UserDetail>
}

Now, you can query a View using this DAO.

回答2:

Absolutely possible, you can use @Query in your DAO class please read Room Database Documentation

Examples of @Query

@Query("SELECT * FROM user")
List<User> getAll();

@Query("SELECT * FROM user WHERE uid IN (:userIds)")
List<User> loadAllByIds(int[] userIds);

@Query("SELECT * FROM user WHERE first_name LIKE :first AND " +
       "last_name LIKE :last LIMIT 1")
User findByName(String first, String last);

回答3:

use @DB or @Query.

That should perfectly work...

@Query("SELECT * FROM TABLE_NAME") List getAll();

来源：https://stackoverflow.com/questions/58297705/search-query-using-android-room-relation

标签

android

android-room