SQL 数据库抽象层 API 库 Swift-Kuery

Swift-Kuery是一个可插拔的SQL数据库驱动程序/ SDK抽象层。 其主要思想是提供一套API，能操作各种关系型数据库，目前支持PostgreSQL、SQLite、MySQL。
虽然Swift-Kuery不是对象关系映射（ORM），但它为构建ORM提供了很大的基础。 如果您不想使用特定的数据库，允许在不同数据库之间轻松切换， Swift-Kuery将会很有用。
示例代码
PostgreSQL数据库中有表格Grades，数据如下：

 id   |  course   | grade
------+-----------+-------
12345 | physics   |    82
12345 | chemistry |    90
12345 | history   |    98
78901 | history   |   100
78901 | chemistry |    94
78901 | physics   |    90
24680 | physics   |    74
24680 | chemistry |    92
24680 | history   |    90

在Swift中创建Grades类，继承Table。

import SwiftKuery
import SwiftKueryPostgreSQL

class Grades: Table {
    let tableName = "Grades"
    let id = Column("id")
    let course = Column("course")
    let grade = Column("grade")
}
let grades = Grades()

连接PostgreSQL 数据库

let pool = PostgreSQLConnection.createPool(host: "localhost", port: 5432, options: [.userName("username"), .password("password")], poolOptions: ConnectionPoolOptions(initialCapacity: 10, maxCapacity: 50, timeout: 10000)))
if let connection = pool.getConnection() {
   // Build and execute your query here.
}
else {
   print("Error: failed to get a connection.")
}

用SQL查询方式如下：

SELECT course, ROUND(AVG(grade), 1) AS "average" FROM grades
GROUP BY course
HAVING AVG(grade) > 90
ORDER BY AVG(grade) ASC

使用Swift-Kuery方式：

let query = Select(grades.course, round(avg(grades.grade), to: 1).as("average"), from: grades)
            .group(by: grades.course)
            .having(avg(grades.grade) > 90)
            .order(by: .ASC(avg(grades.grade)))


guard let connection = pool.getConnection() else {
   // Error
}

connection.execute(query: query) { result: QueryResult in
  if let resultSet = queryResult.asResultSet {
    for title in resultSet.titles {
      // The column names of the result.
    }
    for row in resultSet.rows {
      for value in row {
        ...
      }
    }
  }
  else if let queryError = result.asError {
      // Something went wrong.
  }
}