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我正在使用SQLite-Net Extensions,并且在我对它进行一些操作之前,我想检查一个表是否存在。这是我试过的:如何使用SQLite-Net Extensions进行低级/普通SQL查询?
await this.database.ExecuteScalarAsync<int>("SELECT count(*) FROM sqlite_master WHERE type='table' AND name='{0}'", tableName).ContinueWith(t =>
{
System.Diagnostics.Debug.WriteLine(t.Result);
});
输出是0
。如果我直接在数据库上查询,我会得到一个结果(1
)。然后我试图
var tableQuery = string.Format("SELECT name FROM sqlite_master WHERE type='table' AND name='{0}'", tableName);
var result = await this.database.ExecuteAsync(tableQuery);
,我得到一个异常:
SQLite.SQLiteException: Row
at SQLite.SQLiteCommand.ExecuteNonQuery() [0x0009b] in /Users/fak/Dropbox/Projects/sqlite-net/src/SQLite.cs:2172
at SQLite.SQLiteConnection.Execute (System.String query, System.Object[] args) [0x00040] in /Users/fak/Dropbox/Projects/sqlite-net/src/SQLite.cs:659
at SQLite.SQLiteAsyncConnection+<ExecuteAsync>c__AnonStorey9.<>m__0() [0x00013] in /Users/fak/Dropbox/Projects/sqlite-net/src/SQLiteAsync.cs:222
at System.Threading.Tasks.Task`1[TResult].InnerInvoke() [0x0000f] in <d18287e1d683419a8ec3216fd78947b9>:0
at System.Threading.Tasks.Task.Execute() [0x00010] in <d18287e1d683419a8ec3216fd78947b9>:0
at App.Database+<ClearTable>d__63.MoveNext() [0x00069] in xxx\Database.cs:1011
at App.Util.Helper+<CleanUpTemporaryFiles>d__8.MoveNext() [0x0013a] in xxx\Helper.cs:200
at App.Pages.DetailPage+<OnDisappearing>d__23.MoveNext() [0x000b1] in xxx\DetailPage.xaml.cs:449
对于QueryAsync
你需要用一个参数的构造函数的对象。
现在我不知道如何做一个简单的SELECT
查询。有没有办法得到比更详细的异常信息?
看来你是对的。我把它和'string.Format()'混合在一起。 ExecuteScalarAsync()是检查表是否存在的合适方法吗?除了“ContinueWith”还有其他选择吗? – testing
如果它有效,那对我来说听起来是合理的。 – mjwills