I got a StorageException (ORA-01460) while trying to update string fields in an Oracle 10 database. I tried the same scenario in Sql Server and the in-memory database, no problems there. The error occurs only in very specific circumstances, but I suppose it has something to do with a query parameter that is too small. I made a little app with a very simple model to try some variations. It has a very simple model:

[Serializable]
[HierarchyRoot]
public class MyEntity : Entity
{
    [Field, Key]
    public int Id { get; private set; }

    [Field(Length = 100)]
    public string Text { get; set; }
}

The database is recreated (upgradeMode="Recreate") when the application starts. First, the app create a thousand entities:

using (var transactionScope = Transaction.Open())
{
    for (int i = 1; i <= 1000; i++)
    {
        // new entities, starting with Id == 1
        new MyEntity { Text = "Text" + i.ToString() }; 
    }
    transactionScope.Complete();
}

Then it tries to change the text field of the entities:

// Fails:
using (var transactionScope = Transaction.Open())
{
    for (int i = 1; i <= 10; i++)
    {
        var entity = Query.All<MyEntity>()
                          .Where(e => e.Text == "Text" + i.ToString()).Single();
        entity.Text = "Changed" + i.ToString();
    }
    transactionScope.Complete();
}

This fails because Oracle says that “the requested conversion is not implemented or unreasonable”. The exception details says why:

Error 'Unknown' while executing query 'BEGIN
UPDATE "BOUWGWF"."MYENTITY" SET "TEXT" = :p1_0 WHERE ("MYENTITY"."ID" = :p1_1);
OPEN :p0_c FOR SELECT "a"."ID", "a"."TypeId", "a"."TEXT" FROM (SELECT "b"."ID", 107 AS "TypeId", "b"."TEXT", ROW_NUMBER() OVER(ORDER BY "b"."ID" ASC) AS "RowNumber0" FROM "BOUWGWF"."MYENTITY" "b" WHERE ("b"."TEXT" = :p0_0)) "a" WHERE ("a"."RowNumber0" <= 2);
END; 
[p1_0='Changed9';p1_1='9';p0_0='Text10';p0_c='']'. 
Original message: ORA-01460: Unimplemented or unreasonable conversion requested.

Interestingly, the error occurs for i == 10, and at that moment the length of p0_0 changes. .

Many variations of this scenario do not fail. The number of digits of the lowerbound of the loop has to be smaller than the number of digits of the upperbound.
So “for (int i = 1; i <= 9; i++)”, “for (int i = 10; i <= 99; i++)” and “for (int i = 100; i <= 999; i++)” all work correctly.

There’s also no problem if the loop counts down instead of up: “for (int i = 1000; i >= 1; i--)”

Likewise, if we don’t filter on the Text-property but on the Id, it all works well:

//Succeeds:
using (var transactionScope = Transaction.Open())
{
    for (int i = 1; i <= 1000; i++)
    {
        var entity = Query.All<MyEntity>().Where(e => e.Id == i).Single();
        entity.Text = "Changed" + i.ToString();
    }
    transactionScope.Complete();
}

Finally, unwinding the loop like this gives an exception (as expected):

// Fails
using (var transactionScope = Transaction.Open())
{
        int i = 7; 
        string s1 = "Text" + i.ToString(); string s2 = "Changed" + i.ToString();
        Query.All<MyEntity>().Where(e => e.Text == s1).Single().Text = s2;

        i = 8; 
        s1 = "Text" + i.ToString(); s2 = "Changed" + i.ToString();
        Query.All<MyEntity>().Where(e => e.Text == s1).Single().Text = s2;

        i = 9; 
        s1 = "Text" + i.ToString(); s2 = "Changed" + i.ToString();
        Query.All<MyEntity>().Where(e => e.Text == s1).Single().Text = s2;

        i = 10; 
        s1 = "Text" + i.ToString(); s2 = "Changed" + i.ToString();
        Query.All<MyEntity>().Where(e => e.Text == s1).Single().Text = s2;

        transactionScope.Complete();
}

But if we replace i, s1 and s2 by constants, it suddenly works:

// Succeeds
using (var transactionScope = Transaction.Open())
{
    Query.All<MyEntity>().Where(e => e.Text == "Text7").Single().Text = "Changed7";
    Query.All<MyEntity>().Where(e => e.Text == "Text8").Single().Text = "Changed8";
    Query.All<MyEntity>().Where(e => e.Text == "Text9").Single().Text = "Changed9";
    Query.All<MyEntity>().Where(e => e.Text == "Text10").Single().Text = "Changed10";

    transactionScope.Complete();
}

So, all in all a pretty obscure bug.