6.3 KiB
Q: Squash is same as Exposed. Where is the difference?
A: Ilya Ryzhenkov (Squash maintainer) answers:
Squash is an attempt to refactor Exposed (long time ago) to fix DSL issues, extensibility on dialect side, support graph fetching and avoid TLS-stored transactions. Unfortunately, I didn’t have enough time to finish the work, but I still hope to return to it some day. We are talking with Exposed maintainer @tapac about coordinating efforts and eventually joining forces. Note, that none of these libs are “official” JetBrains Kotlin SQL libs, they are both side projects of their respective authors.
Q: Can I use multiple Database Connections?
A: Yes. See Working with a multiple databases
Q: Is Array column type supported?
A: Not at the moment. More info here: https://github.com/JetBrains/Exposed/issues/150
The complete list of supported data types can be found here: Data Types.
Q: Is upsert supported?
A: Upsert is an instruction to the Database to insert a new row or update existing row based on a table key. It is not supported as part of the library but it is possible to implement on top of it. See this issue: https://github.com/JetBrains/Exposed/issues/167 and example here: https://medium.com/@OhadShai/first-steps-with-kotlin-exposed-cb361a9bf5ac
Q: Is json type supported?
A: Not at the moment. Here is the issue: https://github.com/JetBrains/Exposed/issues/127
The complete list of supported data types can be found here: Data Types.
Q: How to get a plain SQL query which will be executed?
A:
val plainSQL = FooTable.select {}.prepareSQL(QueryBuilder(false))
Use QueryBuiler with false - if you want to inline statement arguments, true - to see '?' in query.
Q: Is it possible to use native sql / sql as a string?
A: It is not supported as part of the library but it is possible to implement on top of it and use it like this:
fun <T:Any> String.execAndMap(transform : (ResultSet) -> T) : List<T> {
val result = arrayListOf<T>()
TransactionManager.current().exec(this) { rs ->
while (rs.next()) {
result += transform(rs)
}
}
return result
}
"select u.name, c.name from user u inner join city c where blah blah".execAndMap { rs ->
rs.getString("u.name") to rs.getString("c.name")
}
More info in this issue: https://github.com/JetBrains/Exposed/issues/118
Q: Is it possible to update a field relative to current field value?
A: Yes. See example here: https://github.com/JetBrains/Exposed/wiki/DSL#update
Q: How can I add another type of Database?
A: Implement DatabaseDialect interface and register it with Database.registerDialect().
If the implementation adds a lot of value consider contributing it as a PR to Exposed.
Q: Is it possible to create tables with cross / cyclic reference?
A: Yes, it's possible since Exposed 0.11.1 version
Q: How can I implement nested queries?
A: See example here: https://github.com/JetBrains/Exposed/issues/248
Q: How can I use SAVEPOINT?
A: It possible only through using a raw connection. See example here.
Q: How to prepare query like: SELECT * FROM table WHERE (x,y) IN ((1, 2), (3, 4), (5, 6))
A: It possible with custom function. See example.
Q: Where can I find snapshot builds of Exposed
A: You could use jitpack.io service for that.
Add jitpack.io to repositories:
repositories {
maven { url 'https://jitpack.io' }
}
Then add Exposed dependency as stated below:
dependencies {
implementation 'com.github.JetBrains:Exposed:-SNAPSHOT'
}
Q: How can I specify a primary key column type e.g StringIdTable?
A: You need to define your own! See examples:
#855
https://stackoverflow.com/a/61940820/1155026
Q: How create custom collumn type
A: Just implements IColumnType and use registerColumn to extends a Table
eg: Create custom UUID types (inpired by @pjagielski article)
abstract class TypedId(open val id: UUID): Serializable, Comparable<TypedId> {
override fun compareTo(other: TypedId) = this.id.compareTo(other.id)
}
class TypedUUIDColumnType<T: TypedId>(val constructor: (UUID) -> T, private val uuidColType: UUIDColumnType = UUIDColumnType()): IColumnType by uuidColType {
override fun valueFromDB(value: Any) = constructor(uuidColType.valueFromDB(value))
override fun notNullValueToDB(value: Any): Any = uuidColType.notNullValueToDB(valueUnwrap(value))
override fun nonNullValueToString(value: Any): String = uuidColType.nonNullValueToString(valueUnwrap(value))
private fun valueUnwrap(value: Any) = (value as? TypedId)?.id ?: value
}
fun <T: TypedId> Table.typedUuid(name: String, constructor: (UUID) -> T) = registerColumn<T>(name, TypedUUIDColumnType<T>(constructor))
fun <T: TypedId> Column<T>.autoGenerate(constructor: (UUID) -> T): Column<T> = clientDefault { constructor(UUID.randomUUID()) }
class StarWarsFilmId(id: UUID): TypedId(id)
object StarWarsFilms : Table() {
val id = typedUuid("id") { StarWarsFilmId(it) }.autoGenerate{ StarWarsFilmId(it) }
val name: Column<String> = varchar("name", 50)
val director: Column<String> = varchar("director", 50)
final override val primaryKey = PrimaryKey(id)
}
Reference: #149