NHibernate and versioning (timestamp)

Question

I got this exception

at System.Convert.ToDateTime(Object value)
at NHibernate.Type.DateTimeType.Get(IDataReader rs, Int32 index) in p:\nhibernate-core\src\NHibernate\Type\DateTimeType.cs:line 43

I guess the error occured when system trying to convert rowversion to datetime

This is my method to get List

public static IList<Employee> getEmployees()
{
    using (ISession mySession = SessionFactory().OpenSession())
    {
        using (ITransaction myTransaction = mySession.BeginTransaction())
        {
            return mySession.CreateCriteria<Employee>().List<Employee>();
        }
    }
}

This is my class

public class Employee {
    private int _id;
    private Rank _rank;
    private string _visa;
    private string _firstName;
    private string _lastName;
    private string _university;
    private DateTime _rowversion;
    public Employee() {
        EmployeeFunctionInProject = new List<EmployeeFunctionInProject>();
        Group = new List<Group>();
    }
    public virtual int Id {
        get {
            return this._id;
        }
        set {
            this._id = value;
        }
    }
    public virtual Rank Rank {
        get {
            return this._rank;
        }
        set {
            this._rank = value;
        }
    }
    public virtual string Visa {
        get {
            return this._visa;
        }
        set {
            this._visa = value;
        }
    }
    public virtual string FirstName {
        get {
            return this._firstName;
        }
        set {
            this._firstName = value;
        }
    }
    public virtual string LastName {
        get {
            return this._lastName;
        }
        set {
            this._lastName = value;
        }
    }
    public virtual string University {
        get {
            return this._university;
        }
        set {
            this._university = value;
        }
    }
    public virtual DateTime Rowversion {
        get {
            return this._rowversion;
        }
        set {
            this._rowversion = value;
        }
    }
    public virtual IList<EmployeeFunctionInProject> EmployeeFunctionInProject { get; set; }
    public virtual IList<Group> Group { get; set; }
}

This is my mapping

<hibernate-mapping assembly="MyWeb11" namespace="MyWeb11.Models" xmlns="urn:nhibernate-mapping-2.2">
  <class name="Employee" table="EMPLOYEE" lazy="true" >
    <id name="Id" column="ID">
      <generator class="identity" />
    </id>
    <many-to-one name="Rank">
      <column name="RANK" sql-type="int" not-null="true" />
    </many-to-one>
    <property name="Visa">
      <column name="VISA" sql-type="varchar" not-null="true" unique="true" />
    </property>
    <property name="FirstName">
      <column name="FIRST_NAME" sql-type="varchar" not-null="true" />
    </property>
    <property name="LastName">
      <column name="LAST_NAME" sql-type="varchar" not-null="true" />
    </property>
    <property name="University">
      <column name="UNIVERSITY" sql-type="varchar" not-null="true" />
    </property>
    <property name="Rowversion">
      <column name="ROWVERSION" sql-type="timestamp" not-null="true" />
    </property>
    <bag name="EmployeeFunctionInProject" inverse="true">
      <key column="EMPLOYEE" />
      <one-to-many class="EmployeeFunctionInProject" />
    </bag>
    <bag name="Group" inverse="true">
      <key column="LEADER" />
      <one-to-many class="Group" />
    </bag>
  </class>
</hibernate-mapping>

I have searched for a solution but haven't found one. Any help is appreciated. Thanks in advance!

score 4 · Accepted Answer · edited May 23 '17 at 12:23

I would expect that you are using SQL Server, where timestamp is not a DateTime value. Nothing in common. See (the up-to-date name is rowversion) - rowversion (Transact-SQL)

Is a data type that exposes automatically generated, unique binary numbers within a database. rowversion is generally used as a mechanism for version-stamping table rows. The storage size is 8 bytes. The rowversion data type is just an incrementing number and does not preserve a date or a time. To record a date or time, use a datetime2 data type.

What I would suggest, do use that type of column (rowversion/timestamp) as you did, with conjunction of NHiberante power of <version> attribute. See:

There is a snippet of the mapping:

<version name="Timestamp " generated="always"
         unsaved-value="null" type="BinaryBlob">
    <column name="Version" not-null="false"
            sql-type="timestamp"/>
</version>

If we need to pass that binary stuff to client we can do some conversion into string property, see:

Optimistic concurrency out of session in NHibernate

property as a C# code:

protected virtual byte[] Timestamp { get; set; }
public virtual string Version
{
    get { return Timestamp.IsEmpty() ? null : Convert.ToBase64String(Timestamp); }
    set { Timestamp = value.IsEmpty() ? null : Convert.FromBase64String(value); }
}

Thanks! I changed from private DateTime _rowversion to private byte[] _rowversion and it works. — haipham23, Jun 05 '14 at 05:32

NHibernate and versioning (timestamp)

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