SQLite error when accessing first element in table using LINQ

问题

I'm having the following issue when accessing a SQLite database using LINQ. Abreviated code looks like this:

...

using System.Linq
using System.Data.Linq
using System.Data.Linq.Mapping
using System.Data.SQLite

...

DataContext sqltContext= new DataContext(sqltConnection);
featureTable = sqltContext.GetTable<FeatureModel>();
count= featureTable.Count(); // count == 1

The following line fails with error: "SQL logic error or missing database\r\nunknown error"

//currentFeature = featureTable.First();

But iterator works fine:

foreach (var feature in featureTable)
{
  currentFeature = feature;
  break;
}

In both cases, I'm getting the following error in debug output:

SQLite error (1): near ".": syntax error

What would cause this error? I'm hoping someone has seen this issue before and can point me in the right direction. But I will probably end up stepping through the System.Data.SQLite code in the debugger at some point.

EDIT: based on comment below from GeorgeT, I added sqltContext.Log = Console.Out;. Based on the logging output, it appears that LINQ is generating a SELECT TOP command, which isn't compatible with SQLite. The solution to this would seem to be to avoid the First or FirstOrDefault methods, or else use something like DBLinq

回答1:

Calling the .First() method generates a SQL query using the SELECT TOP command, which isn't compatible with SQLite. The solution is to avoid using the .First() method, or to use a library which supports LINQ queries to SQLITE, such as DbLinq or LinqConnect.

回答2:

As tdr's answer as mentions .First() generates incorrect SQL and can't be used. I've had to convert the results to a list and then use .First() on the list as a workaround. It won't be very efficient if the results are very large though:

var item = featureTable.ToList().First();

来源：https://stackoverflow.com/questions/23390710/sqlite-error-when-accessing-first-element-in-table-using-linq

标签

linq

sqlite

system.data.sqlite