ios - 在 iOS 应用程序中从 sqlite3 获取没有行

Question

以下代码不返回任何行，但是当我在终端的 sqlite3 中运行查询时，我得到了预期的结果。所以我想这里有一些微不足道的错误:

- (void)initializeDatabaseWithFilter:(NSString *)filter
{
    NSMutableArray *fristArray = [[NSMutableArray alloc] init];
    self.frister = fristArray;
    [fristArray release];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:@"Frister.sqlite"];
    if (sqlite3_open([path UTF8String], &database) == SQLITE_OK){
        // Get primary key for all entries with filter
        const char *sql = "SELECT fristKey FROM frister WHERE ? = 1";
        sqlite3_stmt *statement;
        if (sqlite3_prepare_v2(database, sql, -1, &statement, NULL) != SQLITE_OK) {
            NSAssert1(0,@"Error: Failed to prepare statement with message '%s'.", sqlite3_errmsg(database));
        }
        sqlite3_bind_text(statement, 1, [filter UTF8String], -1, SQLITE_TRANSIENT);
        NSLog(@"%@",filter); // lets me see if the filter column name is passed to the method.
        int i = 0; // this is to see if I get some rows in return
        while (sqlite3_step(statement) == SQLITE_ROW) {
            i++;
            int primaryKey = sqlite3_column_int(statement,0);
            Frist *td = [[Frist alloc] inithWithOwnerID:primaryKey database:database];

            [frister addObject:td];
            [td release];
        }
        NSLog(@"%d",i); // If I get some results, I should get a number here...
        sqlite3_finalize(statement);
    } else {
        sqlite3_close(database);
        NSAssert1(0, @"Failed to open database with message '%s'.", sqlite3_errmsg(database));
    }
}

我真的很想在这里得到一些帮助:)

Answer 1

我看到你已经接受了一个答案，但我想我在你的 sqlite 调用中看到了问题。

在终端中，我猜你正在做这样的查询:

SELECT fristKey FROM frister WHERE column = 1

但是您的代码没有执行等效查询。它正在执行这样的查询:

SELECT fristKey FROM frister WHERE 'column' = 1

由于字符串“column”永远不会等于 1，因此您的查询不会给出任何结果。您不能将列名绑定(bind)到参数化查询中，只能绑定(bind)文字值。