How do I create a private set property on computed (load only) column?

Hello -

I'm running VS2013 Pro and Lightspeed 5, nightly build from June 4. I am using LIghtspeed in a WCF service where the client references the Lightspeed DLLs and Model DLL from the service, copied to a separate directory. I am not using DTOs.

I have a computed column I want to load from a database entity (FullName = FirstName + ' ' + LastName) and forward on to the client. I searched the archives and found several references to computed columns so I made sure to set the field to Load Only = true. However, when I try to forward this entity to the client I get a System.Runtime.Serialization.InvalidDataContractException saying there is no set property for that field.

Digging around in a couple other places (StackOverflow), I learned you need to have a private or protected set property in order for the deserializer to work properly. Lightspeed does not generate this by default. I tried setting the Private Setter option on the column in the designer, but that didn't do anything. When I re-read the comment for the property I can see why, but it was worth a shot.

From what I can tell, the only way to accomplish what I need to do is to set the Generation property to FieldOnly and write custom getter and setter code for the partial class. Really? I would have thought that as slick as this product is you guys would have built in support for this scenario. Is there a better way or is this really how it has to be done?

Thanks for the great product and fantastic support! Dave Newman

Hi Dave,

Yes the approach here is to implement your own property by using the FieldOnly generation option.

Jeremy

Thanks for the confirmation. Any chance this could be a design-level option at some point? I haven't used computed columns prior to this so haven't had the need for it, but it seems this is a common enough usage pattern it might be worth your time and effort to implement designer support for it.

Just sayin' :) Dave

OK so I got most of this working, but Lightspeed seems to still be trying to save the computed column to the database. Here's what I have done so far:

Set Generation to FieldOnly and Load Only to True in the designer.

Here's the code from the model.cs file:

#pragma warning disable 649  // "Field is never assigned to" - LightSpeed assigns these fields internally
[System.Runtime.Serialization.DataMember]
private System.DateTime _createdOn;
[System.Runtime.Serialization.DataMember]
private System.DateTime _updatedOn;
[ValidateLength(0, 61)]
[System.Runtime.Serialization.DataMember]
private string _name;
#pragma warning restore 649    

And here's my custom property:

public partial class Employee
{
    [System.Runtime.Serialization.DataMember]
    public string Name
    {
        get { return _name; }
        protected set { _name = value; }
    }

What am I missing? I'm thinking there should be something in the code, generated or custom, that tells Lightspeed not to persist the field, but I don't see it, and the error I get when trying to save the Employee record tells me it's probably not there:

There was an error processing the request System.Data.SqlClient.SqlException (0x80131904): The column 
"Name" cannot be modified because it is either a computed column or is the result of a UNION operator

Thanks, Dave

Hello? I really need an answer to this and I can't seem to find what I need to do to keep Lightspeed from trying to save the computed column back to the database.

Help! Dave

Hi Dave,

Is the field being generated as readonly? If not does adding the readonly specifier resolve the issue?

Jeremy