Entity Framework mapping issue

alex barylski

Greetings all - I haven't posted here in ages :) I am entirely new to .Net having been working in it for a week at most so please go easy and be detailed as possible :) I have the following PONO:

Public Class WorkOrderEntity

Private intTrackingNumber As Integer
Private intDateReceived As Integer
Private strManufacturer As String

Public Property TrackingNumber() As Integer
    Get
        Return intTrackingNumber
    End Get

    Set(value As Integer)
        intTrackingNumber = value
    End Set
End Property

Public Property DateReceived() As String
    Get
        ' TODO: Convert timestamp to formatted date
        Return intDateReceived
    End Get

    Set(value As String)
        ' TODO: Convert formatted date to timestamp
        intDateReceived = value
    End Set
End Property

End Class

The issue I am faced with is how to store date/time as a timestamp (integer) but provide public properties which format/convert accordingly. I suppose I could provide a an additional getter()/setter() but ideally I wonder if EF has a way of circumventing this "convention"? Additionally - I am also curious as to whether it's possible to map properties to columns which are not labeled correctly? Basically if I were working in a existing database (EF automatically builds my PONO with properties named after table fields) I wish to name the fields something more meaningful; some fields for example might be awkward abbreviations but in the object model I want something more English friendly? I seem to recall being able to do this with Hibernate in java (actually it's PHP port) but never the less does EF support such a feature? Seems obvious that this would be useful in day to day development??? Any ideas? Regards, Alex

Richard Deeming

When you say "timestamp", what do you mean? If it's the SQL timestamp type[^], this has nothing to do with dates:

MSDN:[^]

a data type that exposes automatically generated, unique binary numbers within a database. The timestamp data type is just an incrementing number and does not preserve a date or a time.

You can map a property to a column with a different name using either the Column attribute[^] or the fluent API[^].

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

alex barylski

I just found some articles that explain how to change the mapping for tables so I imagine columns are just around the corner. :) When I say timestamp I mean a unix timestamp which can easily be converted to date AND/OR time - not sure what MSDN is getting at?!? In the database I wish to store the date "10/10/2013" as 1381381200 but convert to a human friendly date within the PONO. My entity objects are high level abstractions but I still prefer to store the time in a numeric format - how does EF solve/address this type mis-match? This is/was the impetus behind OR/M frameworks ain't it? :) Regards, Alex

Richard Deeming

Ah, OK - "timestamp" in SQL is something totally different. I don't think there's any built-in way to perform this sort of conversion in the mapping layer. The simplest approach is probably to add a calculated property for the date, decorated with the NotMapped attribute:

Public Class WorkOrderEntity
Private Shared ReadOnly Epoch As New DateTimeOffset(1970, 1, 1, 0, 0, 0, TimeSpan.Zero)

<Column("DateReceived")> _
Public Property DateReceivedTimestamp() As Integer

<NotMapped> _
Public Property DateReceived() As DateTimeOffset
Get
Return Epoch.AddSeconds(DateReceivedTimestamp)
End Get
Set
DateReceivedTimestamp = CInt(Math.Floor((value - Epoch).TotalSeconds))
End Set
End Property
End Class

I'd be inclined to use DateTimeOffset for the property rather than a string; formatting the date should be a UI concern.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Dave Kreskowiak

EF will see a .NET type of DateTime in your POCO and use the native DateTime datatype specified by the underlying data provider. It will not convert a DateTime to a "serial number" as you want because the serial number can be based on any arbitrary epoch. For example, UNIX uses 1/1/1970 00:00:00AM whereas .NET uses 1/1/0001 00:00:00AM. So, to each system, the datetime serial number will mean something different. Why even do this?? Why not just let the underlying database handle the storage and return the correct datetime without your code having to worry about conversion?

A guide to posting questions on CodeProject[^]
Dave Kreskowiak