When i select from sqlite column of type 'int' I can cast to .net int but when I select from 'integer' column I cannot

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独厮守ぢ
独厮守ぢ 2021-02-09 00:22

I\'m using System.Data.SQLite, selecting from a sqlite database table where a column has type \'integer\', and when I do something like this:

int x = (int)reade         


        
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  • 2021-02-09 00:39

    SQLite http://www.sqlite.org/datatype3.html INTEGER. The value is a signed integer, stored in 1, 2, 3, 4, 6, or 8 bytes depending on the magnitude of the value.

    .NET http://msdn.microsoft.com/en-us/library/cs7y5x0x(VS.90).aspx int -2,147,483,648 .. 2,147,483,647

    So I would expect an overflow or out of range error for 'big' SQlite integer values.

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  • 2021-02-09 00:52

    As the other answerer mentioned, SQLite integer is stored in 1, 2, 3, 4, 6, or 8 bytes. However, you won't get overflow or out of range exceptions.

    In that context, (int) is a cast, not a conversion. If reader[] didn't return an object of type integer, if it's returning a different numeric type, you will get a cast exception, regardless of the value it contains.

    Based on the range of valid values for SQLite integer, I'd guess that it's returning the value as a 64-bit integer, long. To verify, try this:

    object x = reader["myColumn"];
    Debug.WriteLine(x.GetType().Name);
    
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  • 2021-02-09 00:57

    The exception occurs because datareader.Item[] returns object.

    The problem is due to boxing/unboxing. It's nothing to do with the database itself...

    long a = 1; 
    int b = 2; 
    object objectA = a; 
    object objectB = b; 
    Console.WriteLine((int)a); 
    Console.WriteLine((long)b); 
    Console.WriteLine((int)objectA); 
    Console.WriteLine((long)objectB); 
    

    Console outputs 2 then 1, but will throw an exception on the cast of objectA, objectB. This is a characteristic of .NET nothing to do with ODBC drivers.

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