PetaPoco fails inserting record with Guid newid primary key

Question

I'm experimenting with Peta POCO ORM and I quite like it, however there is one thing I can't make work. I'm using MS SQL and table with uniqueidentifier as primary key. However when I insert new record, POCO throws an InvalidCastException trying to cast DBNull to Guid. I created a trivial example. MS SQL table definition :

    CREATE TABLE MyTable
(
    id uniqueidentifier NOT NULL DEFAULT newid(),
    name nvarchar(50) NULL,
    surname nvarchar(50) NULL,
    CONSTRAINT pk_MyTable PRIMARY KEY (id)
)

and then in C# I have:

[PetaPoco.TableName("MyTable")]
[PetaPoco.PrimaryKey("id")]
public class MyTable
{
    public Guid id { get; set; }
    public string name { get; set; }
    public string surname { get; set; }
}

and finally I try to insert new records:

using (var conn = new SqlConnection(myConnString))
{
conn.Open()
using (var db = new PetaPoco.Database(conn))
            {
                for (int i = 0; i < 3; i++)
                {
                    var table = new MyTable() { name = "oh my", surname = i.ToString() };
                    db.Insert(table);
                }
            }
}

Thanks for any help

Answer 1

I believe you need to pre-populate guid type primary key before calling Insert. PetaPoco (at least in V4) support auto filling identity columns after inserts. For guid columns you need to generate guid yourself by calling Guid.NewGuid.

This is not PetaPoco "limitation". SQL Server keeps the last generated identity value in memory which can be retrieved right after an INSERT using SCOPE_IDENTITY(), @@IDENTITY, or CHECK_IDENT (depending on the scope you require). There is nothing similar to capture the last generated GUID value. If you use a GUID, you'll have to create your own mechanism to capture the last inserted value (i.e. retrieve the GUID prior to insertion.

Answer 2

I ran into the same problem trying to insert into a table with a Guid PK. Unfortunately the marked answer alone wasn't enough to fix my issue.

My solution was to do as above setting the Id manually using Guid.NewGuid() but also use the following syntax for the insert. the important bit being the auto increment.

db.Insert("MyTable", "id", false, table);

These arguments map to: table_name, pk_column_name, use_auto_increment, object

Answer 3

This was also my question but I could not find an answer anywhere. So, i found it for myself. Actually, this is a limitation of petapoco since it does not check auto-increment for Guid key.

Let's find the line below in the file PetaPoco.Core.ttinclude:

col.IsAutoIncrement=((int)rdr["IsIdentity"])==1 //This is only check for integer key.

Fix to:

col.IsAutoIncrement=((int)rdr["IsIdentity"])==1 || 
                        (!DBNull.Value.Equals(rdr["DefaultSetting"]) && ((string)rdr["DefaultSetting"] == "(newsequentialid())" ||
                        (string)rdr["DefaultSetting"] == "(newid())")); 

"DefaultSetting" is the default value you set in database for a column. For Guid, it may be newsequentialid() or newid(), it's up to you.