在 Swift 中使用 FMDB 从多个表中进行选择

Question

我正在寻找一种在 Swift 中使用 FMDB 从 7 个不同表中打印出四个特定列的方法。我试过用点符号选择它们，但这似乎不起作用。

数据库看起来像这样：

• 艺术家：[ArtistId]，[姓名]
• 曲目：[TrackId]、[AlbumId]、[Name]
• 专辑：[AlbumId]、[Name]、[ArtistId]
• 类型：[GenreId]，[名称]
• 发票：[CustomerId]、[InvoiceId]
• InvoiceLine：[InvoiceId]
• 客户：[CustomerId]、[FirstName]、[LastName]、[City]

.

import Foundation

let database = FMDatabase(path: " /path to database.sqlite/ ")

database.open()

let rs = try database.executeQuery("SELECT Artist.Name, Track.Name, Album.Title, Genre.Name 
                                    FROM Invoice, Customer, InvoiceLine, Track, Album, Artist, Genre
                                    WHERE Customer.FirstName = 'Michelle'
                                    AND Customer.LastName = 'Brooks' 
                                    AND Customer.City = 'New York'
                                    AND Invoice.CustomerId=Customer.CustomerId 
                                    AND InvoiceLine.InvoiceId = Invoice.InvoiceId 
                                    AND Track.TrackId = InvoiceLine.TrackId 
                                    AND Album.AlbumId = Track.AlbumId 
                                    AND Artist.ArtistId = Album.ArtistId
                                    AND Genre.GenreId = Track.GenreId ", values: nil)

while rs.next() {
    let artistName = rs.stringForColumn("Artist.Name")
    let trackName = rs.stringForColumn("Track.Name")
    let albumTitle = rs.stringForColumn("Album.Title")
    let genre = rs.stringForColumn("Genre.Name")

print (artistName + " " + trackName + " " + albumTitle + " " + genre)
}

Answer 1

问题在于stringForColumn（它使用sqlite_column_name）函数正在使用基础表的列名，而忽略了表名。更糟糕的是，如果你有两列同名，它无法知道你想从哪个表中获取结果。

因此，有两种解决方法：

1. 您可以为列指定唯一名称：

   let rs = try database.executeQuery("SELECT Artist.Name AS ArtistName, Track.Name AS TrackName, Album.Title, Genre.Name AS Genre.Name ..."
   

   然后

   let artistName = rs.stringForColumn("ArtistName")
   let trackName = rs.stringForColumn("TrackName")
   let albumTitle = rs.stringForColumn("Title")
   let genre = rs.stringForColumn("GenreName")
   

   或

2. 使用列号：

   let artistName = rs.stringForColumnIndex(0)
   let trackName = rs.stringForColumnIndex(1)
   let albumTitle = rs.stringForColumnIndex(2)
   let genre = rs.stringForColumnIndex(3)