Dapper: Oracle RAW column to Guid C#: Invalid Cast Exception

[Rojiferio]

Hi,

I'm trying to get Guid columns from Oracle Database (RAW: Generated by Entity Framework code first), and is thrown an exception. Is there some method to achieve it?

Thank you!

[mgravell]

What is the exact error message? I'm hoping it gives a hint as to the data
type coming back. If it is a byte[], and specifically a byte[16], then
yes, I think can can and should support that. If it is something more
exotic... less obvious.

On 3 November 2016 at 09:10, Rojiferio [email protected] wrote:

Hi,

I'm trying to get Guid columns from Oracle Database (RAW: Generated by
Entity Framework code first), and is thrown an exception. Is there some
method to achieve it?

Thank you!

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Marc

[Rojiferio]

Thanks for response,

the error doesn't give me too much information:

Message: "Specified cast is not valid"
Target site: "Deserialize3c1a1cf8-4ac3-44b7-add5-d45d0c40cbfc(System.Data.IDataReader)"

The column is defined as RAW in Oracle, and I want to load in a Guid property. If I get the info using EF works....

Thanks again!

[mgravell]

Can you show me the code that you're using there? Because in many cases, the library injects a lot more context. I'm curious as to why that's being bypassed...

[Rojiferio]

   [TestMethod]
    public void DapperOracle()
    {
        try
        {
            var factProvDb = ProviderDatabaseFactory.GetProviderDatabase("Oracle.ManagedDataAccess.Client", "");
            using (var ctx = DPMContextFactory.CreateDPMContext(factProvDb))
            {
                var sql = @"SELECT * from ""Units""";
                var aux = ctx.Database.Connection.Query<PersistenceModel.Entities.Unit>(sql);
            }
        }
        catch (Exception ex)
        {
            var aux = ex.Message;
        }

    }

And the query should returs that info: (Data columns defined as RAW (16))

[mgravell]

K, I'll see what I can do. There's a slight complication, because .NET Guid does something incredibly stupid I like to call "crazy-endianness", where the byte-order from the byte[]-based methods is essentially random. For giggles. So I need to be very careful to ensure that what we actually get is what you expected.

Here's an illustration:

        var guid = Guid.Parse("00112233-4455-6677-8899-aabbccddeeff");
        var bytes = guid.ToByteArray();

        // shows "33-22-11-00-55-44-77-66-88-99-AA-BB-CC-DD-EE-FF"
        Console.WriteLine(BitConverter.ToString(bytes));
        var guid2 = new Guid(bytes);

        // shows "00112233-4455-6677-8899-aabbccddeeff"
        Console.WriteLine(guid2);

[mormegil-cz]

That is not .NET-specific, is it? That is just native Microsoft GUID format, differing in the endianness of the first three pieces from the RFC 4122 format, AFAICT.

[Rojiferio]

Why method GetGuid is not suported in OracleDataReader Class?????

http://docs.oracle.com/cd/E51173_01/win.122/e17732/OracleDataReaderClass.htm#ODPNT1185

¿is this the problem?

[Rojiferio]

Error parsing column 0 (Id=System.Byte[] - Object)

en Dapper.SqlMapper.ThrowDataException(Exception ex, Int32 index, IDataReader reader, Object value)
en Deserializecf1bf2a6-f889-4904-8c6e-d2c993e5e67d(IDataReader )
en Dapper.SqlMapper.d__1251.MoveNext() en System.Collections.Generic.List1..ctor(IEnumerable1 collection) en System.Linq.Enumerable.ToList[TSource](IEnumerable1 source)
en Dapper.SqlMapper.QueryT
en PersistenceUnitTes

I'm so deseperated...

[mgravell]

I hope to look at this tomorrow.

[mombrea]

I saw your post and was interested. It looks like the answer is that the first 3 sets of the guid are integer types which are independently subject to big endian formatting. The remaining sets of the guid are a byte array and are not subject to endian formatting.

https://msdn.microsoft.com/en-us/library/3573497s.aspx

[mgravell]

I'm have built and uploaded 1.50.3-beta1 that tries to address this. Is there any chance you could try it and let me know if it works?

[Rojiferio]

Thanks!

I expect to can ckeck your release this week , I solved my issue implmenting a custom TypeHandler for Guid:

class GuidTypeHandler : SqlMapper.TypeHandler<Guid> { public override Guid Parse(object value) { var inVal = (byte[])value; return new Guid(inVal); }

With this code I can read data without problem.

I'll answer you as soon as possible.

Thank you again!

[NickCraver]

@Rojiferio just looking to close this out if we're all good here - can you please let us know when you get a chance? Thanks!

[mgravell]

I need to revert
https://github.com/StackExchange/dapper-dot-net/commit/91725fb309a9e5948f760fac420dd805659f0749;
the upshot if this is that there is no reliable cross-provider mechanism
that works well for this.

On 3 Dec 2016 12:36 p.m., "Nick Craver" [e-mail] wrote:

@Rojiferio https://github.com/Rojiferio just looking to close this out
if we're all good here - can you please let us know when you get a
chance? Thanks!

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[mgravell]

Reverted; sorry, closing this down since we can't support it natively in the lib due to the incompatibility between backends