在 Swift 中使用 FMDB 从多个表中进行选择
SELECTing from multiple tables with FMDB in Swift
我正在寻找一种方法来使用 Swift 中的 FMDB 从 7 个不同的表中打印出四个特定的列。我试过用点符号来选择它们,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]、[名称]
- 专辑:[AlbumId]、[Name]、[ArtistId]
- 流派:[GenreId]、[名称]
- 发票:[CustomerId]、[InvoiceId]
- 发票行:[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)
}
问题是 stringForColumn
(使用 sqlite_column_name
)函数使用基础 table 的列的名称而忽略了 table.更糟糕的是,如果您有两列同名的列,它无法知道您希望从哪个 table 获得结果。
因此,有两种解决方法:
您可以为列指定唯一的名称:
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
使用列号:
let artistName = rs.stringForColumnIndex(0)
let trackName = rs.stringForColumnIndex(1)
let albumTitle = rs.stringForColumnIndex(2)
let genre = rs.stringForColumnIndex(3)
我正在寻找一种方法来使用 Swift 中的 FMDB 从 7 个不同的表中打印出四个特定的列。我试过用点符号来选择它们,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]、[名称]
- 专辑:[AlbumId]、[Name]、[ArtistId]
- 流派:[GenreId]、[名称]
- 发票:[CustomerId]、[InvoiceId]
- 发票行:[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)
}
问题是 stringForColumn
(使用 sqlite_column_name
)函数使用基础 table 的列的名称而忽略了 table.更糟糕的是,如果您有两列同名的列,它无法知道您希望从哪个 table 获得结果。
因此,有两种解决方法:
您可以为列指定唯一的名称:
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
使用列号:
let artistName = rs.stringForColumnIndex(0) let trackName = rs.stringForColumnIndex(1) let albumTitle = rs.stringForColumnIndex(2) let genre = rs.stringForColumnIndex(3)