Exposed Kotlin 的轻量级 ORM

Exposed 是 Kotlin 实现的轻量级 ORM，也是 JetBrains 和 Kotlin 官方倾力推荐的 ORM。

该 ORM 十分轻量级，只做了底层封装、Dao 基础和 Model 基础，中上层的封装完全没有，可嵌入 Spring。

目前支持的数据库方言：

PostgreSQL

MySQL

Oracle

SQLite

H2

SQL Server

推荐一个 starter 项目：Kotlin + Ktor + Exposed

示例代码

SQL DSL 示例：

importorg.jetbrains.exposed.sql.*importorg.jetbrains.exposed.sql.transactions.transactionobjectUsers:Table(){valid=varchar("id",10).primaryKey()//Column<String>valname=varchar("name",length=50)//Column<String>valcityId=(integer("city_id")referencesCities.id).nullable()//Column<Int?>}objectCities:Table(){valid=integer("id").autoIncrement().primaryKey()//Column<Int>valname=varchar("name",50)//Column<String>}funmain(args:Array<String>){Database.connect("jdbc:h2:mem:test",driver="org.h2.Driver")transaction{SchemaUtils.create(Cities,Users)valsaintPetersburgId=Cities.insert{it[name]="St.Petersburg"}getCities.idvalmunichId=Cities.insert{it[name]="Munich"}getCities.idCities.insert{it[name]="Prague"}Users.insert{it[id]="andrey"it[name]="Andrey"it[cityId]=saintPetersburgId}Users.insert{it[id]="sergey"it[name]="Sergey"it[cityId]=munichId}Users.insert{it[id]="eugene"it[name]="Eugene"it[cityId]=munichId}Users.insert{it[id]="alex"it[name]="Alex"it[cityId]=null}Users.insert{it[id]="smth"it[name]="Something"it[cityId]=null}Users.update({Users.ideq"alex"}){it[name]="Alexey"}Users.deleteWhere{Users.namelike"%thing"}println("Allcities:")for(cityinCities.selectAll()){println("${city[Cities.id]}:${city[Cities.name]}")}println("Manualjoin:")(UsersinnerJoinCities).slice(Users.name,Cities.name).select{(Users.id.eq("andrey")orUsers.name.eq("Sergey"))andUsers.id.eq("sergey")andUsers.cityId.eq(Cities.id)}.forEach{println("${it[Users.name]}livesin${it[Cities.name]}")}println("Joinwithforeignkey:")(UsersinnerJoinCities).slice(Users.name,Users.cityId,Cities.name).select{Cities.name.eq("St.Petersburg")orUsers.cityId.isNull()}.forEach{if(it[Users.cityId]!=null){println("${it[Users.name]}livesin${it[Cities.name]}")}else{println("${it[Users.name]}livesnowhere")}}println("Functionsandgroupby:")((CitiesinnerJoinUsers).slice(Cities.name,Users.id.count()).selectAll().groupBy(Cities.name)).forEach{valcityName=it[Cities.name]valuserCount=it[Users.id.count()]if(userCount>0){println("$userCountuser(s)live(s)in$cityName")}else{println("Nobodylivesin$cityName")}}SchemaUtils.drop(Users,Cities)}}

Outputs:

SQL:CREATETABLEIFNOTEXISTSCities(idINTAUTO_INCREMENTNOTNULL,nameVARCHAR(50)NOTNULL,CONSTRAINTpk_CitiesPRIMARYKEY(id))SQL:CREATETABLEIFNOTEXISTSUsers(idVARCHAR(10)NOTNULL,nameVARCHAR(50)NOTNULL,city_idINTNULL,CONSTRAINTpk_UsersPRIMARYKEY(id))SQL:ALTERTABLEUsersADDFOREIGNKEY(city_id)REFERENCESCities(id)SQL:INSERTINTOCities(name)VALUES('St.Petersburg')SQL:INSERTINTOCities(name)VALUES('Munich')SQL:INSERTINTOCities(name)VALUES('Prague')SQL:INSERTINTOUsers(id,name,city_id)VALUES('andrey','Andrey',1)SQL:INSERTINTOUsers(id,name,city_id)VALUES('sergey','Sergey',2)SQL:INSERTINTOUsers(id,name,city_id)VALUES('eugene','Eugene',2)SQL:INSERTINTOUsers(id,name,city_id)VALUES('alex','Alex',NULL)SQL:INSERTINTOUsers(id,name,city_id)VALUES('smth','Something',NULL)SQL:UPDATEUsersSETname='Alexey'WHEREUsers.id='alex'SQL:DELETEFROMUsersWHEREUsers.nameLIKE'%thing'Allcities:SQL:SELECTCities.id,Cities.nameFROMCities1:St.Petersburg2:Munich3:PragueManualjoin:SQL:SELECTUsers.name,Cities.nameFROMUsersINNERJOINCitiesONCities.id=Users.city_idWHERE((Users.id='andrey')or(Users.name='Sergey'))andUsers.id='sergey'andUsers.city_id=Cities.idSergeylivesinMunichJoinwithforeignkey:SQL:SELECTUsers.name,Users.city_id,Cities.nameFROMUsersINNERJOINCitiesONCities.id=Users.city_idWHERE(Cities.name='St.Petersburg')or(Users.city_idISNULL)AndreylivesinSt.PetersburgFunctionsandgroupby:SQL:SELECTCities.name,COUNT(Users.id)FROMCitiesINNERJOINUsersONCities.id=Users.city_idGROUPBYCities.name1user(s)live(s)inSt.Petersburg2user(s)live(s)inMunichSQL:DROPTABLEUsersSQL:DROPTABLECities