如何使用IN条件访问SQLite.swift中的FTS表

Question

我正在尝试使用SQLite.swift查询FTS表。 Previously I have done it in Android。我想要做的事情的本质是this：

SELECT *
FROM t2
WHERE id IN (SELECT docid
             FROM fts_table
             WHERE col_text MATCH 'something')

从SQLite.swift documentation我看到IN condition可以写成this：

users.filter([1, 2, 3, 4, 5].contains(id))
// SELECT * FROM "users" WHERE ("id" IN (1, 2, 3, 4, 5))

可以像this一样查询虚拟表：

let wonderfulEmails = emails.match("wonder*")
// SELECT * FROM "emails" WHERE "emails" MATCH 'wonder*'

let replies = emails.filter(subject.match("Re:*"))
// SELECT * FROM "emails" WHERE "subject" MATCH 'Re:*'

但是，我无法弄清楚如何将这些结合起来。我真的不想要execute arbitrary SQL（虽然现在正在努力，感谢this answer的帮助）。

更新

这是我最近的尝试不起作用：

let tableText = Table("t2")
let id = Expression<Int64>("id")
let someColumn = Expression<String>("someColumn")

let tableFts = VirtualTable("fts_table")
let columnDocId = Expression<Int64>("docId")


let ftsQuery = tableFts
    .select(columnDocId)
    .filter(tableFts.match("something"))
let tableQuery = tableText
    .filter((try db.prepare(ftsQuery))
        .contains(id))                       // <-- error

for row in try db.prepare(tableQuery) {
    print(row[someColumn])
}

与contains(id)的行抛出错误：

无法将'Expression'类型的值转换为预期的参数类型'@noescape（Row）throws - > Bool'

Answer 1

我最终只是运行原始SQL命令。这并不完全回答我在问题中提出的问题（因为它不使用纯SQLite.swift API），但对于那些只需要工作的人来说，......它的工作原理。

这是我从一些源代码中提取的修改示例。

static func findLinesContaining(_ searchTerms: String, forSearchScope scope: SearchScope) throws -> [TextLines] {

    guard let db = SQLiteDataStore.sharedInstance.TextDB else {
        throw DataAccessError.datastore_Connection_Error
    }

    // TODO: convert to SQLite.swift syntax rather than using a SQL string
    var statement: Statement? = nil
    switch scope {
    case .wholeCollection:
        statement = try db.run("SELECT bookId, chapterId, lineId, lineText" +
            " FROM lines" +
            " WHERE rowid IN (SELECT docid FROM fts_table" +
            " WHERE fts_table MATCH ?);", searchTerms)

    case .singleBook(let chosenBookId):
        statement = try db.run("SELECT bookId, chapterId, lineId, lineText" +
            " FROM lines" +
            " WHERE rowid IN (SELECT docid FROM fts_table" +
            " WHERE fts_table MATCH ?) AND bookId = ?;", [searchTerms, chosenBookId])
    }


    var returnList: [TextLine] = []
    for row in statement! {

        let line = TextLine()
        if let bookId = row[0] as? Int64,
            let chapterId = row[1] as? Int64,
            let lineId = row[2] as? Int64,
            let text = row[3] as? String {

            line.bookId = Int(bookId)
            line.chapterId = Int(chapterId)
            line.lineId = Int(lineId)
            line.lineText = text
        }

        returnList.append(line)
    }

    return returnList
}

重命名变量和类以在SO上使用后，上述代码未经测试。如果您发现错误，您有权编辑代码。