我正在为新项目使用空间,但是我在为如何干净地访问一对一值而苦苦挣扎
我有地址,所有者和站点的实体,所有者和站点都有一个关联的地址,并且每个站点都有一个所有者
是否可以干净地访问这些文件,例如site.owner.address.l1
?
我查看了@Relation
,尽管它返回的列表不理想
实体
@Entity(tableName="addresses")
data class Address(
@PrimaryKey
@ColumnInfo(name="address_id")
val id: Int,
@ColumnInfo(name="address_l1")
val l1: String
)
@Entity(tablename="owners")
data class Owner(
@PrimaryKey
@ColumnInfo(name="owner_id")
val id: Int,
@ColumnInfo(name="owner_name")
val name: String
)
@Entity(tableName="sites")
data class Site(
@PrimaryKey
@ColumnInfo(name="site_id")
val id: Int,
@ColumnInfo(name="site_addressid")
val addressid: Int
@ColumnInfo(name="site_ownerid")
val ownerid: Int
)
道氏
@Query("SELECT * FROM sites")
fun getSites(): List<Site>
@Query("SELECT * FROM owners")
fun getOwners(): List<Owner>
@Query("SELECT * FROM addresses")
fun getAddresses(): List<Address>
@Query("SELECT * FROM sites JOIN address ON sites.site_addressid = address.address_id JOIN owners ON sites.site_ownerid = owners.owner_id JOIN address ON owners.owner_addressid = address.address_id WHERE sites.site_id = :siteid")
fun getSiteByIdWithDetails(siteid): Site
我只能看到多个POJO的方法来完成这项工作,例如
无效,但大致正确
data class OwnerAddress(
@Embedded
val owner: Owner,
@Embedded
val address: Address
)
data class SiteAddress(
@Embedded
val site: Site,
@Embedded
val owner: OwnerAddress,
@Embedded
val address: Address
}
并通过使用它
@Query("SELECT * FROM sites JOIN address ON sites.site_addressid = address.address_id JOIN owners ON sites.site_ownerid = owners.owner_id JOIN address ON owners.owner_addressid = address.address_id WHERE sites.site_id = :siteid")
fun getSiteByIdWithDetails(siteid): SiteAddress
最佳答案
您是否尝试过在实体之间建立关系? Android Documentation for Relationships
@Entity(tableName="addresses")
data class Address(
@PrimaryKey
@ColumnInfo(name="address_id")
val id: Int,
@ColumnInfo(name="address_l1")
val l1: String
)
@Entity(tablename="owners")
data class Owner(
@PrimaryKey
@ColumnInfo(name="owner_id")
val id: Int,
@ColumnInfo(name="owner_name")
val name: String
@ColumnInfo(name="owner_adress")
@Entity val adress: Address
)
@Entity(tableName="sites")
data class Site(
@PrimaryKey
@ColumnInfo(name="site_id")
val id: Int,
@ColumnInfo(name="site_owner")
@Embedded val owner: Owner
@ColumnInfo(name="site_address")
@Embedded val address: Address
)
因此,现在您的站点具有一个地址和一个所有者(具有其地址)。您的
sites
表和owners
表都将包含“地址”列。
关于database - Android Room数据库: How to embed multiple entities,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51860810/