我正在从两个表查询并将数据组合到一个POJO。
我有一个带有一些条目的表和一个带有类别的表。
我正在查询以下语句：
@Transaction
@Query("SELECT $BOOKENTRIES.*, $CATEGORIES.$ID AS $PREFIX_CATEGORY$ID, $CATEGORIES.$NAME AS $PREFIX_CATEGORY$NAME, $CATEGORIES.$ICON_ID AS $PREFIX_CATEGORY$ICON_ID, $CATEGORIES.$COLOR AS $PREFIX_CATEGORY$COLOR FROM $BOOKENTRIES INNER JOIN $CATEGORIES ON $BOOKENTRIES.$CATEGORY_ID = $CATEGORIES.$ID WHERE $BOOKENTRIES.$ID = :id")
fun get(id: Long): BookEntry?
$BOOKENTRIES.$CATEGORY_ID列可以为null。
如果删除与内部join语句有关的所有内容，则查询有效。
POJO：
class BookEntry(
@Embedded var entity: BookEntryEntity = BookEntryEntity(),
@Embedded(prefix = PREFIX_CATEGORY) var category: Category? = null,
contacts: List<Contact.ContactEntity>? = null
) : Parcelable {
@Relation(
entity = Contact.ContactEntity::class,
parentColumn = ID,
entityColumn = BOOKENTRY_ID
)
var embeddedContacts: List<Contact.ContactEntity>? = contacts
var id: Long
get() = entity.id
set(value) {
entity.id = value
}
var title: String
get() = entity.title
set(value) {
entity.title = value
}
var date: Date
get() = entity.date
set(value) {
entity.date = value
}
var value: Double
get() = entity.value
set(value) {
entity.value = value
}
var notes: String
get() = entity.notes
set(value) {
entity.notes = value
}
var entryType: Int
get() = entity.entryType
set(value) {
entity.entryType = value
}
fun contacts(context: Context, onFinish: (List<Contact>?) -> Unit) = GlobalScope.launch(Dispatchers.Main) {
onFinish(contacts(context))
}
suspend fun contacts(context: Context): List<Contact>? = withContext(Dispatchers.IO) {
return@withContext context.hasPermission(Manifest.permission.READ_CONTACTS).takeIf { it }?.run {
embeddedContacts?.map {
Contact(it.id, it.bookEntryId, it.contactId, ContactsLoader(context).loadContactName(it.contactId), it.hasPaid)
} ?: listOf()
}
}
val isClaimOrDebt: Boolean
get() = entryType == Type.Claim || entryType == Type.Debt
object Type {
const val Earning = 0
const val Expense = 1
const val Claim = 2
const val Debt = 3
}
@Entity(tableName = Database.Table.BOOKENTRIES)
data class BookEntryEntity(
@PrimaryKey(autoGenerate = true) @ColumnInfo(name = ID) var id: Long = 0,
@ColumnInfo(name = TITLE) var title: String = "",
@ColumnInfo(name = DATE) var date: Date = Date(),
@ColumnInfo(name = VALUE) var value: Double = 0.0,
@ColumnInfo(name = NOTES) var notes: String = "",
@ColumnInfo(name = ENTRYTYPE) var entryType: Int = Type.Earning,
@ColumnInfo(name = CATEGORY_ID) var categoryId: Long? = null
) : Parcelable {
constructor(parcel: Parcel) : this(
parcel.readLong(),
parcel.readString() as String,
Date(parcel.readLong()),
parcel.readDouble(),
parcel.readString() as String,
parcel.readInt()
)
override fun writeToParcel(parcel: Parcel, flags: Int) {
parcel.writeLong(id)
parcel.writeString(title)
parcel.writeLong(date.time)
parcel.writeDouble(value)
parcel.writeString(notes)
parcel.writeInt(entryType)
}
override fun describeContents(): Int {
return 0
}
companion object CREATOR : Parcelable.Creator<BookEntryEntity> {
override fun createFromParcel(parcel: Parcel): BookEntryEntity {
return BookEntryEntity(parcel)
}
override fun newArray(size: Int): Array<BookEntryEntity?> {
return arrayOfNulls(size)
}
}
}
//region Parcelable
constructor(parcel: Parcel) : this(
parcel.readParcelable(BookEntryEntity::class.java.classLoader) as BookEntryEntity,
parcel.readParcelable(Category::class.java.classLoader),
parcel.createTypedArrayList(Contact.ContactEntity)
)
override fun writeToParcel(parcel: Parcel, flags: Int) {
parcel.writeParcelable(entity, flags)
parcel.writeParcelable(category, flags)
parcel.writeList(embeddedContacts)
}
override fun describeContents(): Int {
return 0
}
//endregion
companion object {
fun create(id: Long = 0, title: String, date: Date, value: Double, notes: String, entryType: Int, categoryId: Long? = null, contacts: List<Contact.ContactEntity>? = null): BookEntry {
return BookEntry(BookEntryEntity(id = id, title = title, date = date, value = value, notes = notes, entryType = entryType, categoryId = categoryId), contacts = contacts)
}
fun createClaimEntry(title: String, date: Date, value: Double, notes: String, categoryId: Long? = null, contacts: List<Contact.ContactEntity>?): BookEntry {
return create(title = title, date = date, value = value, notes = notes, entryType = Type.Claim, categoryId = categoryId, contacts = contacts)
}
fun createDebtEntry(title: String, date: Date, value: Double, notes: String, categoryId: Long? = null, contacts: List<Contact.ContactEntity>?): BookEntry {
return create(title = title, date = date, value = value, notes = notes, entryType = Type.Debt, categoryId = categoryId, contacts = contacts)
}
@JvmField
val CREATOR = object : Parcelable.Creator<BookEntry> {
override fun createFromParcel(parcel: Parcel): BookEntry {
return BookEntry(parcel)
}
override fun newArray(size: Int): Array<BookEntry?> {
return arrayOfNulls(size)
}
}
}
}
类别实体：
@Entity(tableName = Database.Table.CATEGORIES)
data class Category(
@PrimaryKey(autoGenerate = true) @ColumnInfo(name = ID) var id: Long = 0,
@ColumnInfo(name = NAME) var name: String = "",
@ColumnInfo(name = ICON_ID) var iconId: Int = 0,
@ColumnInfo(name = COLOR) @ColorInt var color: Int = DEFAULT_COLOR
) : Parcelable {
constructor(parcel: Parcel) : this(
parcel.readLong(),
parcel.readString() as String,
parcel.readInt()
)
override fun writeToParcel(parcel: Parcel, flags: Int) {
parcel.writeLong(id)
parcel.writeString(name)
parcel.writeInt(iconId)
}
override fun describeContents(): Int {
return 0
}
companion object {
@JvmField
val CREATOR = object : Parcelable.Creator<Category> {
override fun createFromParcel(parcel: Parcel): Category {
return Category(parcel)
}
override fun newArray(size: Int): Array<Category?> {
return arrayOfNulls(size)
}
}
}
}
以及数据库的架构：
"entities": [
{
"tableName": "bookentries",
"createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `title` TEXT NOT NULL, `date` INTEGER NOT NULL, `value` REAL NOT NULL, `notes` TEXT NOT NULL, `entrytype` INTEGER NOT NULL, `category_id` INTEGER)",
"fields": [
{
"fieldPath": "id",
"columnName": "id",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "title",
"columnName": "title",
"affinity": "TEXT",
"notNull": true
},
{
"fieldPath": "date",
"columnName": "date",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "value",
"columnName": "value",
"affinity": "REAL",
"notNull": true
},
{
"fieldPath": "notes",
"columnName": "notes",
"affinity": "TEXT",
"notNull": true
},
{
"fieldPath": "entryType",
"columnName": "entrytype",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "categoryId",
"columnName": "category_id",
"affinity": "INTEGER",
"notNull": false
}
],
"primaryKey": {
"columnNames": [
"id"
],
"autoGenerate": true
},
"indices": [],
"foreignKeys": []
},
{
"tableName": "categories",
"createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `name` TEXT NOT NULL, `icon_id` INTEGER NOT NULL, `color` INTEGER NOT NULL)",
"fields": [
{
"fieldPath": "id",
"columnName": "id",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "name",
"columnName": "name",
"affinity": "TEXT",
"notNull": true
},
{
"fieldPath": "iconId",
"columnName": "icon_id",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "color",
"columnName": "color",
"affinity": "INTEGER",
"notNull": true
}
],
"primaryKey": {
"columnNames": [
"id"
],
"autoGenerate": true
},
"indices": [],
"foreignKeys": []
},
{
"tableName": "bookentrycontacts",
"createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `bookentry_id` INTEGER NOT NULL, `contact_id` INTEGER NOT NULL, `has_paid` INTEGER NOT NULL, FOREIGN KEY(`bookentry_id`) REFERENCES `bookentries`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE )",
"fields": [
{
"fieldPath": "id",
"columnName": "id",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "bookEntryId",
"columnName": "bookentry_id",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "contactId",
"columnName": "contact_id",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "hasPaid",
"columnName": "has_paid",
"affinity": "INTEGER",
"notNull": true
}
],
"primaryKey": {
"columnNames": [
"id"
],
"autoGenerate": true
},
"indices": [
{
"name": "index_bookentrycontacts_bookentry_id",
"unique": false,
"columnNames": [
"bookentry_id"
],
"createSql": "CREATE INDEX `index_bookentrycontacts_bookentry_id` ON `${TABLE_NAME}` (`bookentry_id`)"
}
],
"foreignKeys": [
{
"table": "bookentries",
"onDelete": "CASCADE",
"onUpdate": "NO ACTION",
"columns": [
"bookentry_id"
],
"referencedColumns": [
"id"
]
}
]
},
{
"tableName": "reminders",
"createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `bookentry_id` INTEGER NOT NULL, `worker_uuid` TEXT NOT NULL, `date` INTEGER NOT NULL, FOREIGN KEY(`bookentry_id`) REFERENCES `bookentries`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE )",
"fields": [
{
"fieldPath": "id",
"columnName": "id",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "bookEntryId",
"columnName": "bookentry_id",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "workerUUID",
"columnName": "worker_uuid",
"affinity": "TEXT",
"notNull": true
},
{
"fieldPath": "fireDate",
"columnName": "date",
"affinity": "INTEGER",
"notNull": true
}
],
"primaryKey": {
"columnNames": [
"id"
],
"autoGenerate": true
},
"indices": [
{
"name": "index_reminders_bookentry_id",
"unique": true,
"columnNames": [
"bookentry_id"
],
"createSql": "CREATE UNIQUE INDEX `index_reminders_bookentry_id` ON `${TABLE_NAME}` (`bookentry_id`)"
}
],
"foreignKeys": [
{
"table": "bookentries",
"onDelete": "CASCADE",
"onUpdate": "NO ACTION",
"columns": [
"bookentry_id"
],
"referencedColumns": [
"id"
]
}
]
}
]
这是什么问题？
答案 0 :(得分：0)
因此，我查看了您提到的以下查询，它对我来说看起来不错：
SELECT $BOOKENTRIES.*, $CATEGORIES.$ID AS $PREFIX_CATEGORY$ID,
$CATEGORIES.$NAME AS $PREFIX_CATEGORY$NAME, $CATEGORIES.$ICON_ID AS
$PREFIX_CATEGORY$ICON_ID, $CATEGORIES.$COLOR AS $PREFIX_CATEGORY$COLOR FROM
$BOOKENTRIES INNER JOIN $CATEGORIES ON $BOOKENTRIES.$CATEGORY_ID =
$CATEGORIES.$ID WHERE $BOOKENTRIES.$ID = :id
能否请您分享表，以便我为您提供确切的答案。好吧，现在您能在没有过滤器的情况下尝试再次尝试吗？
SELECT $BOOKENTRIES.*, $CATEGORIES.$ID AS $PREFIX_CATEGORY$ID,
$CATEGORIES.$NAME AS $PREFIX_CATEGORY$NAME, $CATEGORIES.$ICON_ID AS
$PREFIX_CATEGORY$ICON_ID, $CATEGORIES.$COLOR AS $PREFIX_CATEGORY$COLOR FROM
$BOOKENTRIES INNER JOIN $CATEGORIES ON $BOOKENTRIES.$CATEGORY_ID =
$CATEGORIES.$ID
答案 1 :(得分：0)
我将查询更改为以下内容：
@Transaction
@Query("SELECT $BOOKENTRIES.*, $CATEGORIES.$ID AS $PREFIX_CATEGORY$ID, $CATEGORIES.$NAME AS $PREFIX_CATEGORY$NAME, $CATEGORIES.$ICON_ID AS $PREFIX_CATEGORY$ICON_ID, $CATEGORIES.$COLOR AS $PREFIX_CATEGORY$COLOR FROM $BOOKENTRIES LEFT JOIN $CATEGORIES ON $BOOKENTRIES.$CATEGORY_ID = $CATEGORIES.$ID WHERE $BOOKENTRIES.$ID = :id")
fun get(id: Long): BookEntry?
由于我要从表“ b”加载数据作为表“ a”的附加信息，因此必须使用LEFT JOIN。 （请参阅https://stackoverflow.com/a/6188334/5994190）
答案 2 :(得分：0)
问题似乎是您的Categories表为空。然后，使用内部联接不会获得任何结果。您想要的是外部联接。在这种情况下，左联接。将INNER替换为LEFT，然后看看会得到什么。