Kotlin Exposed Patterns

Kotlin Exposed 模式

使用 JetBrains Exposed ORM 进行数据库访问的全面模式，包括 DSL 查询、DAO、事务以及生产就绪的配置。

何时使用

• 使用 Exposed 设置数据库访问
• 使用 Exposed DSL 或 DAO 编写 SQL 查询
• 使用 HikariCP 配置连接池
• 使用 Flyway 创建数据库迁移
• 使用 Exposed 实现仓储模式
• 处理 JSON 列和复杂查询

工作原理

Exposed 提供两种查询风格：用于直接类似 SQL 表达式的 DSL 和用于实体生命周期管理的 DAO。HikariCP 通过 HikariConfig 配置来管理可重用的数据库连接池。Flyway 在启动时运行版本化的 SQL 迁移脚本以保持模式同步。所有数据库操作都在 newSuspendedTransaction 块内运行，以确保协程安全和原子性。仓储模式将 Exposed 查询包装在接口之后，使业务逻辑与数据层解耦，并且测试可以使用内存中的 H2 数据库。

示例

DSL 查询

suspend fun findUserById(id: UUID): UserRow? =
    newSuspendedTransaction {
        UsersTable.selectAll()
            .where { UsersTable.id eq id }
            .map { it.toUser() }
            .singleOrNull()
    }

DAO 实体用法

suspend fun createUser(request: CreateUserRequest): User =
    newSuspendedTransaction {
        UserEntity.new {
            name = request.name
            email = request.email
            role = request.role
        }.toModel()
    }

HikariCP 配置

val hikariConfig = HikariConfig().apply {
    driverClassName = config.driver
    jdbcUrl = config.url
    username = config.username
    password = config.password
    maximumPoolSize = config.maxPoolSize
    isAutoCommit = false
    transactionIsolation = "TRANSACTION_READ_COMMITTED"
    validate()
}

数据库设置

HikariCP 连接池

// DatabaseFactory.kt
object DatabaseFactory {
    fun create(config: DatabaseConfig): Database {
        val hikariConfig = HikariConfig().apply {
            driverClassName = config.driver
            jdbcUrl = config.url
            username = config.username
            password = config.password
            maximumPoolSize = config.maxPoolSize
            isAutoCommit = false
            transactionIsolation = "TRANSACTION_READ_COMMITTED"
            validate()
        }

        return Database.connect(HikariDataSource(hikariConfig))
    }
}

data class DatabaseConfig(
    val url: String,
    val driver: String = "org.postgresql.Driver",
    val username: String = "",
    val password: String = "",
    val maxPoolSize: Int = 10,
)

Flyway 迁移

// FlywayMigration.kt
fun runMigrations(config: DatabaseConfig) {
    Flyway.configure()
        .dataSource(config.url, config.username, config.password)
        .locations("classpath:db/migration")
        .baselineOnMigrate(true)
        .load()
        .migrate()
}

// Application startup
fun Application.module() {
    val config = DatabaseConfig(
        url = environment.config.property("database.url").getString(),
        username = environment.config.property("database.username").getString(),
        password = environment.config.property("database.password").getString(),
    )
    runMigrations(config)
    val database = DatabaseFactory.create(config)
    // ...
}

迁移文件

-- src/main/resources/db/migration/V1__create_users.sql
CREATE TABLE users (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name VARCHAR(100) NOT NULL,
    email VARCHAR(255) NOT NULL UNIQUE,
    role VARCHAR(20) NOT NULL DEFAULT 'USER',
    metadata JSONB,
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

CREATE INDEX idx_users_email ON users(email);
CREATE INDEX idx_users_role ON users(role);

表定义

DSL 风格表

// tables/UsersTable.kt
object UsersTable : UUIDTable("users") {
    val name = varchar("name", 100)
    val email = varchar("email", 255).uniqueIndex()
    val role = enumerationByName<Role>("role", 20)
    val metadata = jsonb<UserMetadata>("metadata", Json.Default).nullable()
    val createdAt = timestampWithTimeZone("created_at").defaultExpression(CurrentTimestampWithTimeZone)
    val updatedAt = timestampWithTimeZone("updated_at").defaultExpression(CurrentTimestampWithTimeZone)
}

object OrdersTable : UUIDTable("orders") {
    val userId = uuid("user_id").references(UsersTable.id)
    val status = enumerationByName<OrderStatus>("status", 20)
    val totalAmount = long("total_amount")
    val currency = varchar("currency", 3)
    val createdAt = timestampWithTimeZone("created_at").defaultExpression(CurrentTimestampWithTimeZone)
}

object OrderItemsTable : UUIDTable("order_items") {
    val orderId = uuid("order_id").references(OrdersTable.id,
    val productId = uuid("product_id")
    val quantity = integer("quantity")
    val unitPrice = long("unit_price")
}

复合表

object UserRolesTable : Table("user_roles") {
    val userId = uuid("user_id").references(UsersTable.id,
    val roleId = uuid("role_id").references(RolesTable.id,
    override val primaryKey = PrimaryKey(userId, roleId)
}

DSL 查询

基本 CRUD

// Insert
suspend fun insertUser(name: String, email: String, role: Role): UUID =
    newSuspendedTransaction {
        UsersTable.insertAndGetId {
            it[UsersTable.name] = name
            it[UsersTable.email] = email
            it[UsersTable.role] = role
        }.value
    }

// Select by ID
suspend fun findUserById(id: UUID): UserRow? =
    newSuspendedTransaction {
        UsersTable.selectAll()
            .where { UsersTable.id eq id }
            .map { it.toUser() }
            .singleOrNull()
    }

// Select with conditions
suspend fun findActiveAdmins(): List<UserRow> =
    newSuspendedTransaction {
        UsersTable.selectAll()
            .where { (UsersTable.role eq Role.ADMIN) }
            .orderBy(UsersTable.name)
            .map { it.toUser() }
    }

// Update
suspend fun updateUserEmail(id: UUID, newEmail: String): Boolean =
    newSuspendedTransaction {
        UsersTable.update({ UsersTable.id eq id }) {
            it[email] = newEmail
            it[updatedAt] = CurrentTimestampWithTimeZone
        } > 0
    }

// Delete
suspend fun deleteUser(id: UUID): Boolean =
    newSuspendedTransaction {
        UsersTable.deleteWhere { UsersTable.id eq id } > 0
    }

// Row mapping
private fun ResultRow.toUser() = UserRow(
    id = this[UsersTable.id].value,
    name = this[UsersTable.name],
    email = this[UsersTable.email],
    role = this[UsersTable.role],
    metadata = this[UsersTable.metadata],
    createdAt = this[UsersTable.createdAt],
    updatedAt = this[UsersTable.updatedAt],
)

高级查询

// Join queries
suspend fun findOrdersWithUser(userId: UUID): List<OrderWithUser> =
    newSuspendedTransaction {
        (OrdersTable innerJoin UsersTable)
            .selectAll()
            .where { OrdersTable.userId eq userId }
            .orderBy(OrdersTable.createdAt, SortOrder.DESC)
            .map { row ->
                OrderWithUser(
                    orderId = row[OrdersTable.id].value,
                    status = row[OrdersTable.status],
                    totalAmount = row[OrdersTable.totalAmount],
                    userName = row[UsersTable.name],
                )
            }
    }

// Aggregation
suspend fun countUsersByRole(): Map<Role, Long> =
    newSuspendedTransaction {
        UsersTable
            .select(UsersTable.role, UsersTable.id.count())
            .groupBy(UsersTable.role)
            .associate { row ->
                row[UsersTable.role] to row[UsersTable.id.count()]
            }
    }

// Subqueries
suspend fun findUsersWithOrders(): List<UserRow> =
    newSuspendedTransaction {
        UsersTable.selectAll()
            .where {
                UsersTable.id inSubQuery
                    OrdersTable.select(OrdersTable.userId).withDistinct()
            }
            .map { it.toUser() }
    }

// LIKE and pattern matching — always escape user input to prevent wildcard injection
private fun escapeLikePattern(input: String): String =
    input.replace("\\", "\\\\").replace("%", "\\%").replace("_", "\\_")

suspend fun searchUsers(query: String): List<UserRow> =
    newSuspendedTransaction {
        val sanitized = escapeLikePattern(query.lowercase())
        UsersTable.selectAll()
            .where {
                (UsersTable.name.lowerCase() like "%${sanitized}%") or
                    (UsersTable.email.lowerCase() like "%${sanitized}%")
            }
            .map { it.toUser() }
    }

分页

data class Page<T>(
    val data: List<T>,
    val total: Long,
    val page: Int,
    val limit: Int,
) {
    val totalPages: Int get() = ((total + limit - 1) / limit).toInt()
    val hasNext: Boolean get() = page < totalPages
    val hasPrevious: Boolean get() = page > 1
}

suspend fun findUsersPaginated(page: Int, limit: Int): Page<UserRow> =
    newSuspendedTransaction {
        val total = UsersTable.selectAll().count()
        val data = UsersTable.selectAll()
            .orderBy(UsersTable.createdAt, SortOrder.DESC)
            .limit(limit)
            .offset(((page - 1) * limit).toLong())
            .map { it.toUser() }

        Page(data = data, total = total, page = page, limit = limit)
    }

批量操作

// Batch insert
suspend fun insertUsers(users: List<CreateUserRequest>): List<UUID> =
    newSuspendedTransaction {
        UsersTable.batchInsert(users) { user ->
            this[UsersTable.name] = user.name
            this[UsersTable.email] = user.email
            this[UsersTable.role] = user.role
        }.map { it[UsersTable.id].value }
    }

// Upsert (insert or update on conflict)
suspend fun upsertUser(id: UUID, name: String, email: String) {
    newSuspendedTransaction {
        UsersTable.upsert(UsersTable.email) {
            it[UsersTable.id] = EntityID(id, UsersTable)
            it[UsersTable.name] = name
            it[UsersTable.email] = email
            it[updatedAt] = CurrentTimestampWithTimeZone
        }
    }
}

DAO 模式

实体定义

// entities/UserEntity.kt
class UserEntity(id: EntityID<UUID>) : UUIDEntity(id) {
    companion object : UUIDEntityClass<UserEntity>(UsersTable)

    var name by UsersTable.name
    var email by UsersTable.email
    var role by UsersTable.role
    var metadata by UsersTable.metadata
    var createdAt by UsersTable.createdAt
    var updatedAt by UsersTable.updatedAt

    val orders by OrderEntity referrersOn OrdersTable.userId

    fun toModel(): User = User(
        id = id.value,
        name = name,
        email = email,
        role = role,
        metadata = metadata,
        createdAt = createdAt,
        updatedAt = updatedAt,
    )
}

class OrderEntity(id: EntityID<UUID>) : UUIDEntity(id) {
    companion object : UUIDEntityClass<OrderEntity>(OrdersTable)

    var user by UserEntity referencedOn OrdersTable.userId
    var status by OrdersTable.status
    var totalAmount by OrdersTable.totalAmount
    var currency by OrdersTable.currency
    var createdAt by OrdersTable.createdAt

    val items by OrderItemEntity referrersOn OrderItemsTable.orderId
}

DAO 操作

suspend fun findUserByEmail(email: String): User? =
    newSuspendedTransaction {
        UserEntity.find { UsersTable.email eq email }
            .firstOrNull()
            ?.toModel()
    }

suspend fun createUser(request: CreateUserRequest): User =
    newSuspendedTransaction {
        UserEntity.new {
            name = request.name
            email = request.email
            role = request.role
        }.toModel()
    }

suspend fun updateUser(id: UUID, request: UpdateUserRequest): User? =
    newSuspendedTransaction {
        UserEntity.findById(id)?.apply {
            request.name?.let { name = it }
            request.email?.let { email = it }
            updatedAt = OffsetDateTime.now(ZoneOffset.UTC)
        }?.toModel()
    }

事务

挂起事务支持

// Good: Use newSuspendedTransaction for coroutine support
suspend fun performDatabaseOperation(): Result<User> =
    runCatching {
        newSuspendedTransaction {
            val user = UserEntity.new {
                name = "Alice"
                email = "alice@example.com"
            }
            // All operations in this block are atomic
            user.toModel()
        }
    }

// Good: Nested transactions with savepoints
suspend fun transferFunds(fromId: UUID, toId: UUID, amount: Long) {
    newSuspendedTransaction {
        val from = UserEntity.findById(fromId) ?: throw NotFoundException("User $fromId not found")
        val to = UserEntity.findById(toId) ?: throw NotFoundException("User $toId not found")

        // Debit
        from.balance -= amount
        // Credit
        to.balance += amount

        // Both succeed or both fail
    }
}

事务隔离级别

suspend fun readCommittedQuery(): List<User> =
    newSuspendedTransaction(transactionIsolation = Connection.TRANSACTION_READ_COMMITTED) {
        UserEntity.all().map { it.toModel() }
    }

suspend fun serializableOperation() {
    newSuspendedTransaction(transactionIsolation = Connection.TRANSACTION_SERIALIZABLE) {
        // Strictest isolation level for critical operations
    }
}

仓储模式

接口定义

interface UserRepository {
    suspend fun findById(id: UUID): User?
    suspend fun findByEmail(email: String): User?
    suspend fun findAll(page: Int, limit: Int): Page<User>
    suspend fun search(query: String): List<User>
    suspend fun create(request: CreateUserRequest): User
    suspend fun update(id: UUID, request: UpdateUserRequest): User?
    suspend fun delete(id: UUID): Boolean
    suspend fun count(): Long
}

Exposed 实现

class ExposedUserRepository(
    private val database: Database,
) : UserRepository {

    override suspend fun findById(id: UUID): User? =
        newSuspendedTransaction(db = database) {
            UsersTable.selectAll()
                .where { UsersTable.id eq id }
                .map { it.toUser() }
                .singleOrNull()
        }

    override suspend fun findByEmail(email: String): User? =
        newSuspendedTransaction(db = database) {
            UsersTable.selectAll()
                .where { UsersTable.email eq email }
                .map { it.toUser() }
                .singleOrNull()
        }

    override suspend fun findAll(page: Int, limit: Int): Page<User> =
        newSuspendedTransaction(db = database) {
            val total = UsersTable.selectAll().count()
            val data = UsersTable.selectAll()
                .orderBy(UsersTable.createdAt, SortOrder.DESC)
                .limit(limit)
                .offset(((page - 1) * limit).toLong())
                .map { it.toUser() }
            Page(data = data, total = total, page = page, limit = limit)
        }

    override suspend fun search(query: String): List<User> =
        newSuspendedTransaction(db = database) {
            val sanitized = escapeLikePattern(query.lowercase())
            UsersTable.selectAll()
                .where {
                    (UsersTable.name.lowerCase() like "%${sanitized}%") or
                        (UsersTable.email.lowerCase() like "%${sanitized}%")
                }
                .orderBy(UsersTable.name)
                .map { it.toUser() }
        }

    override suspend fun create(request: CreateUserRequest): User =
        newSuspendedTransaction(db = database) {
            UsersTable.insert {
                it[name] = request.name
                it[email] = request.email
                it[role] = request.role
            }.resultedValues!!.first().toUser()
        }

    override suspend fun update(id: UUID, request: UpdateUserRequest): User? =
        newSuspendedTransaction(db = database) {
            val updated = UsersTable.update({ UsersTable.id eq id }) {
                request.name?.let { name -> it[UsersTable.name] = name }
                request.email?.let { email -> it[UsersTable.email] = email }
                it[updatedAt] = CurrentTimestampWithTimeZone
            }
            if (updated > 0) findById(id) else null
        }

    override suspend fun delete(id: UUID): Boolean =
        newSuspendedTransaction(db = database) {
            UsersTable.deleteWhere { UsersTable.id eq id } > 0
        }

    override suspend fun count(): Long =
        newSuspendedTransaction(db = database) {
            UsersTable.selectAll().count()
        }

    private fun ResultRow.toUser() = User(
        id = this[UsersTable.id].value,
        name = this[UsersTable.name],
        email = this[UsersTable.email],
        role = this[UsersTable.role],
        metadata = this[UsersTable.metadata],
        createdAt = this[UsersTable.createdAt],
        updatedAt = this[UsersTable.updatedAt],
    )
}

JSON 列

使用 kotlinx.serialization 的 JSONB

// Custom column type for JSONB
inline fun <reified T : Any> Table.jsonb(
    name: String,
    json: Json,
): Column<T> = registerColumn(name, object : ColumnType<T>() {
    override fun sqlType() = "JSONB"

    override fun valueFromDB(value: Any): T = when (value) {
        is String -> json.decodeFromString(value)
        is PGobject -> {
            val jsonString = value.value
                ?: throw IllegalArgumentException("PGobject value is null for column '$name'")
            json.decodeFromString(jsonString)
        }
        else -> throw IllegalArgumentException("Unexpected value: $value")
    }

    override fun notNullValueToDB(value: T): Any =
        PGobject().apply {
            type = "jsonb"
            this.value = json.encodeToString(value)
        }
})

// Usage in table
@Serializable
data class UserMetadata(
    val preferences: Map<String, String> = emptyMap(),
    val tags: List<String> = emptyList(),
)

object UsersTable : UUIDTable("users") {
    val metadata = jsonb<UserMetadata>("metadata", Json.Default).nullable()
}

使用 Exposed 进行测试

用于测试的内存数据库

class UserRepositoryTest : FunSpec({
    lateinit var database: Database
    lateinit var repository: UserRepository

    beforeSpec {
        database = Database.connect(
            url = "jdbc:h2:mem:test;DB_CLOSE_DELAY=-1;MODE=PostgreSQL",
            driver = "org.h2.Driver",
        )
        transaction(database) {
            SchemaUtils.create(UsersTable)
        }
        repository = ExposedUserRepository(database)
    }

    beforeTest {
        transaction(database) {
            UsersTable.deleteAll()
        }
    }

    test("create and find user") {
        val user = repository.create(CreateUserRequest("Alice", "alice@example.com"))

        user.name shouldBe "Alice"
        user.email shouldBe "alice@example.com"

        val found = repository.findById(user.id)
        found shouldBe user
    }

    test("findByEmail returns null for unknown email") {
        val result = repository.findByEmail("unknown@example.com")
        result.shouldBeNull()
    }

    test("pagination works correctly") {
        repeat(25) { i ->
            repository.create(CreateUserRequest("User $i", "user$i@example.com"))
        }

        val page1 = repository.findAll(page = 1, limit = 10)
        page1.data shouldHaveSize 10
        page1.total shouldBe 25
        page1.hasNext shouldBe true

        val page3 = repository.findAll(page = 3, limit = 10)
        page3.data shouldHaveSize 5
        page3.hasNext shouldBe false
    }
})

Gradle 依赖项

// build.gradle.kts
dependencies {
    // Exposed
    implementation("org.jetbrains.exposed:exposed-core:1.0.0")
    implementation("org.jetbrains.exposed:exposed-dao:1.0.0")
    implementation("org.jetbrains.exposed:exposed-jdbc:1.0.0")
    implementation("org.jetbrains.exposed:exposed-kotlin-datetime:1.0.0")
    implementation("org.jetbrains.exposed:exposed-json:1.0.0")

    // Database driver
    implementation("org.postgresql:postgresql:42.7.5")

    // Connection pooling
    implementation("com.zaxxer:HikariCP:6.2.1")

    // Migrations
    implementation("org.flywaydb:flyway-core:10.22.0")
    implementation("org.flywaydb:flyway-database-postgresql:10.22.0")

    // Testing
    testImplementation("com.h2database:h2:2.3.232")
}

快速参考：Exposed 模式

记住：对于简单查询使用 DSL 风格，当需要实体生命周期管理时使用 DAO 风格。始终使用 newSuspendedTransaction 以获得协程支持，并将数据库操作包装在仓储接口之后以提高可测试性。

原文

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