鉴于有 3 张 table
@Entity
data class Pet(
@PrimaryKey
val id: String,
val name: String,
val colour: String,
height: Int
ownerId: String,
householdId: String
)
@Entity
data class Owner(
@PrimaryKey
val id: String,
val name: String,
val address: String,
val telephoneNumer: Int
)
@Entity
data class Household(
@PrimaryKey
val id: String,
val name: String,
val address: String,
val region: String
)
执行返回 Pet
中的所有条目的查询的最佳方式是什么? , Owner
和 Household
在哪里 name
包含“Dav”并获取与此类似的数据列表(为简洁起见,减去一些字段)
Pet("Dave"...) // Pet
Owner("David"...) //Owner
Owner("Davina"...) //Owner
Household("Davenport Close"...) //Address
最佳答案
如果您想要的只是一个 LIST,那么您可以使用自定义 POJO 和使用 UNION 的查询。
例如,您可以有一个 POJO,例如:-
data class searchPOJO(
val id: String,
val type: String,
val name: String
)
和一个查询,例如:- @Query("SELECT id,'Pet' AS type,name FROM pet WHERE name LIKE :search UNION SELECT id, 'owner' AS type, name FROM owner WHERE name LIKE :search UNION SELECT id, 'household' AS type, name FROM household WHERE name LIKE :search")
abstract fun search(search: String): List<searchPOJO>
你会像这样调用它:-dao.search("%dav%")
例如以下代码:-
db = TheDatabase.getInstance(this)
dao = db.getAllDao()
dao.insert(Pet("pet1","Dave","brown",10,"Fred","1 Maria Cresent"))
dao.insert(Pet("pet2","George","red",11,"Bert","2 Somewhere Place"))
dao.insert(Owner("owner1","David","10 Somewhere Place",1111111111))
dao.insert(Owner("owner2","Laura","14 Overthere Way", 222222222))
dao.insert(Owner("owner3","Davina","3 Wayland Way",333333333))
dao.insert(Household("h1","Davenport Close","1 Davenport Close","region 1"))
dao.insert(Household("h2","Daintree House","100 Smith Street","region 2"))
for(s: searchPOJO in dao.search("%dav%")) {
Log.d("DBINFO","ID is ${s.id} Name is ${s.name} Type is ${s.type}")
}
结果是 :-D/DBINFO: ID is h1 Name is Davenport Close Type is household
D/DBINFO: ID is owner1 Name is David Type is owner
D/DBINFO: ID is owner3 Name is Davina Type is owner
D/DBINFO: ID is pet1 Name is Dave Type is Pet
如果您想要在每次查找时返回每个对象中的一个(1 个有效对象和其他 2 个无效对象(例如空白))并指示返回的类型,那么您可以使用类似以下的 POJO:-data class searchPOJOAll (
val type: String,
@Embedded(prefix = Companion.pet_prefix)
val pet: Pet,
@Embedded(prefix = owner_prefix)
val owner: Owner,
@Embedded(prefix = household_prefix)
val household: Household
) {
companion object {
const val pet_prefix: String = "pet_"
const val owner_prefix: String = "owner_"
const val household_prefix: String = "household_"
}
}
然后,查询将是先前查询的扩展版本,三个 SELECTS 中的每一个都为其他对象提供列,由于需要消除列名的歧义,这再次变得复杂,例如:-
@Query("SELECT 'PET' AS type, " +
" id AS " + searchPOJOAll.pet_prefix + "id," +
" name AS " + searchPOJOAll.pet_prefix + "name," +
" colour AS " + searchPOJOAll.pet_prefix + "colour," +
" height AS " + searchPOJOAll.pet_prefix + "height," +
" ownerId AS " + searchPOJOAll.pet_prefix + "ownerId," +
" householdId AS " + searchPOJOAll.pet_prefix + "householdId," +
" '' AS " + searchPOJOAll.owner_prefix + "id," +
" '' AS " + searchPOJOAll.owner_prefix + "name," +
" '' AS " + searchPOJOAll.owner_prefix + "address," +
" '' AS " + searchPOJOAll.owner_prefix + "telephoneNumer," +
" '' AS " + searchPOJOAll.household_prefix + "id," +
" '' AS " + searchPOJOAll.household_prefix + "name," +
" '' AS " + searchPOJOAll.household_prefix + "address," +
" '' AS " + searchPOJOAll.household_prefix + "region" +
" FROM pet WHERE name LIKE :search " +
" UNION SELECT 'OWNER' AS type, " +
" '' AS " + searchPOJOAll.pet_prefix + "id," +
" '' AS " + searchPOJOAll.pet_prefix + "name," +
" '' AS " + searchPOJOAll.pet_prefix + "colour," +
" '' AS " + searchPOJOAll.pet_prefix + "height," +
" '' AS " + searchPOJOAll.pet_prefix + "ownerId," +
" '' AS " + searchPOJOAll.pet_prefix + "householdId," +
" id AS " + searchPOJOAll.owner_prefix + "id," +
" name AS " + searchPOJOAll.owner_prefix + "name," +
" address AS " + searchPOJOAll.owner_prefix + "address," +
" telephoneNumer AS " + searchPOJOAll.owner_prefix + "telephoneNumer," +
" '' AS " + searchPOJOAll.household_prefix + "id," +
" '' AS " + searchPOJOAll.household_prefix + "name," +
" '' AS " + searchPOJOAll.household_prefix + "address," +
" '' AS " + searchPOJOAll.household_prefix + "region" +
" FROM owner WHERE name LIKE :search " +
" UNION SELECT 'HOUSEHOLD' AS type," +
" '' AS " + searchPOJOAll.pet_prefix + "id," +
" '' AS " + searchPOJOAll.pet_prefix + "name," +
" '' AS " + searchPOJOAll.pet_prefix + "colour," +
" '' AS " + searchPOJOAll.pet_prefix + "height," +
" '' AS " + searchPOJOAll.pet_prefix + "ownerId," +
" '' AS " + searchPOJOAll.pet_prefix + "householdId," +
" '' AS " + searchPOJOAll.owner_prefix + "id," +
" '' AS " + searchPOJOAll.owner_prefix + "name," +
" '' AS " + searchPOJOAll.owner_prefix + "address," +
" '' AS " + searchPOJOAll.owner_prefix + "telephoneNumer," +
" id AS " + searchPOJOAll.household_prefix + "id," +
" name AS " + searchPOJOAll.household_prefix + "name," +
" address AS " + searchPOJOAll.household_prefix + "address," +
" region AS " + searchPOJOAll.household_prefix + "region" +
" FROM household WHERE name LIKE :search"
)
abstract fun searchAll(search: String): List<searchPOJOAll>
扩展之前的演示代码:- /* List of all 3 object types (only one of which is of use) */
for(s: searchPOJOAll in dao.searchAll("%dav%")) {
if(s.type == "PET") {
Log.d("DBINFO","${s.type}>>>" + getPetString(s.pet))
}
if (s.type == "OWNER") {
Log.d("DBINFO","${s.type}>>>" + getOwnerString(s.owner))
}
if (s.type == "HOUSEHOLD") {
Log.d("DBINFO","${s.type}>>>" +getHouseholdString(s.household))
}
}
并具有以下功能:-fun getPetString(pet: Pet):String {
return "ID is ${pet.id} Petname = ${pet.name} colour is ${pet.colour} height is ${pet.height} ownerID is ${pet.ownerId} householId is ${pet.householdId}"
}
fun getOwnerString(owner: Owner): String {
return "ID is ${owner.id} Ownername is ${owner.name} address is ${owner.address} telno is ${owner.telephoneNumer}"
}
fun getHouseholdString(household: Household): String {
return "ID is ${household.id} name is ${household.name} address is ${household.address} region is ${household.region}"
}
结果(对于相同的数据)将是:-D/DBINFO: HOUSEHOLD>>>ID is h1 name is Davenport Close address is 1 Davenport Close region is region 1
D/DBINFO: OWNER>>>ID is owner1 Ownername is David address is 10 Somewhere Place telno is 1111111111
D/DBINFO: OWNER>>>ID is owner3 Ownername is Davina address is 3 Wayland Way telno is 333333333
D/DBINFO: PET>>>ID is pet1 Petname = Dave colour is brown height is 10 ownerID is Fred householId is 1 Maria Cresent
尽管根据评论Android文档中提供的示例似乎创建了一个新的组合模型,而不是使用POJO从上述3个表中返回单独的实体,例如:-data class PetWithOwnerAndHousehold (
@Embedded
val pet: Pet,
@Relation( entity = Owner::class, parentColumn = "ownerId",entityColumn = "id")
val owner: Owner,
@Relation(entity = Household::class, parentColumn = "householdId", entityColumn = "id")
val household: Household
)
和一个查询/道,例如:-@Query("SELECT pet.* FROM pet JOIN owner ON owner.id = pet.ownerId JOIN household ON household.id = pet.householdId WHERE pet.name LIKE :search OR owner.name LIKE :search OR household.name LIKE :search")
abstract fun getPetWithOwnerAndHousehold(search: String): List<PetWithOwnerAndHousehold>
将返回宠物、它的所有者和它的 houdehold(假设关系(pet->owener 和 pet->houdhold)是有效的(在上面的数据中它们不是))如果是 pat 名称、所有者的姓名或家庭名称匹配搜索项。例如如果添加了以下行(使用现有的所有者和 houdeholds):-
dao.insert(Pet("p1","adava","grey",12,"owner1","h2")) /* multiple hits pet name and owner name*/
dao.insert(Pet("p2","lady","blue",13,"owner2","h2")) /* no hits */
dao.insert(Pet("p3","X","pink",14,"owner2","h1")) /* one hit household name */
然后使用 查询的结果%dav% 因为搜索字符串是:-D/DBINFO: Pet ID is p1 pet's name is adava OwnerID is owner1 owner's name is David etc. HouseholdID is h2 household's name is Daintree House
D/DBINFO: Pet ID is p3 pet's name is X OwnerID is owner2 owner's name is Laura etc. HouseholdID is h1 household's name is Davenport Close
关于android - 使用单个查询在 Android Room 中搜索多个表,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/69245197/