NHibernate MappingException: no persister for byte[]

Question

I'm using NHibernate to store downloads in my MySQL database for an ASP.NET MVC website. I am using to classes. One called Download for the download itself and one called DownloadContent for the file itself (so I can load it easier when I just want to get the metadata).

The data class declarations and mappings look like this:

public class Download
{
    public virtual string Id { get; set; }
    public virtual string OutFileName { get; set; }
    public virtual DownloadContent Contents { get; set; }
    public virtual string MimeType { get; set; }
    public virtual bool DoForward { get; set; }
    public virtual string RedirectLink { get; set; }
}

public class DownloadMap : ClassMap<Download>
{
    public DownloadMap()
    {
        Id(x => x.Id);
        Map(x => x.OutFileName);
        References<DownloadContent>(x => x.Contents);
        Map(x => x.MimeType);
        Map(x => x.DoForward).Not.Nullable();
        Map(x => x.RedirectLink);
    }
}

public class DownloadContent
{
    public virtual byte[] Data { get; set; }
}

public class DownloadContentMap : ClassMap<DownloadContent>
{
    public DownloadContentMap()
    {
        Id();
        Map(x => x.Data).CustomType("BinaryBlob");
    }
}

Now, when I try to do like this:

dl.Contents = new DownloadContent { Data = content };
db.session.SaveOrUpdate(content);

I get an NHibernate.MappingException with the message "No persister for: System.Byte[]". I looked it up with the NHibernate docs and byte[] should map correctly.

What am I doing wrong?

Florian Lim · Accepted Answer · 2011-03-31T21:25:24.277

2

If I read that correctly you are actually trying to save the byte[] to the DB, which can't work, since byte[] is not a mapped entity.

You probably want to write:

dl.Contents = new DownloadContent { Data = content };
db.session.SaveOrUpdate(dl); // content is wrong, since content is of type byte[]

Also, since you didn't specify an Inverse(), you will probably have to SaveOrUpdate the DownloadContent first, therefore:

Download dl = new Download { OutFileName = "Test", DoForward = true };
DownloadContent dlc = new DownloadContent { Data = content };
dl.Contents = dlc;
db.session.SaveOrUpdate(dlc);
db.session.SaveOrUpdate(dl);

edited Mar 31 '11 at 21:25

answered Mar 31 '11 at 21:02

Florian Lim

5,332
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@DontCare4Free Your code says `db.session.SaveOrUpdate(content);` Unless that's a typo or I am missing something, "content" is of type byte[], which you cannot pass as a parameter to `SaveOrUpdate()` – Florian Lim Mar 31 '11 at 21:24
It is a wrapper around the type byte[]. – Teo Klestrup Röijezon Mar 31 '11 at 21:59
@DontCare4Free Wrapper or not, the error `No persister for: System.Byte[]` is definitely pointing to the fact, that your parameter in `SaveOrUpdate()` is of type byte[]. Please try to replace that line with `db.session.SaveOrUpdate(dl);` – Florian Lim Mar 31 '11 at 22:08

score 2 · Answer 2 · edited Mar 31 '11 at 21:14

You specified a CustomType of BinaryBlob. NHibernate will look for an IUserType called BinaryBlob to perform the persistence. I think you want CustomSqlType to say that MySQL should use its BinaryBlob type in the database.

public class DownloadContentMap : ClassMap<DownloadContent>
{
    public DownloadContentMap()
    {
        Id();
        Map(x => x.Data).CustomSqlType("BinaryBlob");
    }
}

NHibernate MappingException: no persister for byte[]

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