在SQLite.swift中从具有正确绑定的任意SQL语句获取结果 [英] Getting results from arbitrary SQL statements with correct binding in SQLite.swift

问题描述

SQLite.swift文档关于执行任意SQL:

The SQLite.swift documentation says about executing arbitrary SQL:

let stmt = try db.prepare("SELECT id, email FROM users")
for row in stmt {
    for (index, name) in stmt.columnNames.enumerate() {
        print ("\(name)=\(row[index]!)")
        // id: Optional(1), email: Optional("[e-mail]")
    }
}

我想像这样直接获取值

let stmt = try db.prepare("SELECT id, email FROM users")
for row in stmt {
    let myInt: Int64 = row[0] // error: Cannot convert value of type 'Binding?' to specified type 'Int64'
    let myString: String = row[1] // error: Cannot convert value of type 'Binding?' to specified type 'String'
}

，但行索引的类型为Binding?，我不知道如何将其转换为所需的类型.我看到源代码中有一个Statement.bind方法，但是我仍然没有发现如何应用它.

but the row index is of type Binding? and I can't figure out how to convert that to the type I need. I see there is a Statement.bind method in the source code but I am still not discovering how to apply it.

推荐答案

您可以从像这样的表中检索正确键入的所选列:

You can retrieve correctly typed selected columns from a table like this:

// The database.
let db = try Connection(...)

// The table.
let users = Table("users")

// Typed column expressions.
let id = Expression<Int64>("id")
let email = Expression<String>("email")

// The query: "SELECT id, email FROM users"
for user in try db.prepare(users.select(id, email)) {
    let id = user[id]       // Int64
    let mail = user[email]  // String
    print(id, mail)
}

一种替代方法是(可选)强制转换Binding值 正确的类型:

An alternative is to (optionally) cast the Binding values to the correct type:

let stmt = try db.prepare("SELECT id, email FROM users")
for row in stmt {
    if let id = row[0] as? Int64,
        let mail = row[1] as? String {
        print(id, mail)
    }
}

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