Background

Microsoft’s LightSwitch is marketed as this easy to use tool, but I am finding it as a great easy to confuse tool.

 

Problem Identification

GUI

I have a simple Data Entry GUI that looks like this:

I am being asked to enter the “added By” name.

Usually I will check on the database’s stored procedure and set it to SYSTEM_USER when empty.

Data Model

BTW, here is the entity..

We can see that “addedBy” is a String and it is Required.

Unfortunately, I am not able to toggle the required flag as it is greyed out.

 

 

Remediation

Entity – properties – Allow Empty String

Property Changes

Here is our first remediation try …

The “Is Required” flag is disabled.  And, so took the easy route of checking the “Allow Empty String” flag.

And, so now that we are “Allowing Empty String”, I feel good.

Trial

Tried it out and here is where that got me…

GUI

Textual

Failed to load model: Model Error: Could not resolve id ‘:@AllowEmptyString’ to a model item.

 

Solve the error message

Guide

The rest of the afternoon was spent googling for this incredibly useful error message

Failed to load model: Model Error: Could not resolve is ‘:@AllowEmptyString’ to a model item.

Best idea comes through Dave Baker and it is pasted here:

 

Here are the steps:

1. Launch your favorite editor
2. Identify the lsml file
   • Syntax
     • [Project]\[Project].HTMLClient\Properties\<datasource>\[entity].lsml
   • Sample
     • EDiag\EDiag.HTMLClient\Properties\DBDiagData\listofContacts.lsml
3. Comment out the DiscardFromCollection element

 

Guide

Faulty

 

Revised

 

Entity – properties – Default to single space

Guide

The alternate route is to revisit our entity and take the following steps:

1. Supporting Work
   1. Unfortunately, Javascript does not provide a user’s name
   2. We have to get on the Server Side
   3. To get it on the Server side we have to tighten things up and require Windows or Forms Authentication
2.  Entity
   • For the Entity provide code for setting the front-end default value
   • And, if need be the actual backend value

 

Project Properties

From the Solution Explorer, choose the Project, and right click on it

Default Screen

Here is the default setting

Explanation

1. The default choice is not to enable authentication

 

Revised Screen

 

Explanation

1. The Authentication Type is
   • Use Windows authentication
   • We have two choices
     • Allow only users and Active Directory security groups specified in the Users screen of the application
     • Allow any authenticated Windows user
   • We chose to “Allow any authenticated Windows user” as this is just a mock up

 

Entity

1. Access the HTMLClient Tab
   • Choose “Write Code“
   • For the Created Event
     • And, enter a code that supplies a place holder (space) for our property
2. Access the Server Tab
   • Choose “Write Code“
   • In the Inserting Event
     • Check if field is still at default, if so calculate value and overwrite default

HTMLClient

 

 

Code

/// <reference path="~/GeneratedArtifacts/viewModel.js" />

myapp.listofContact.created = function (entity) {
 // Write code here.

 entity.active = true;
 entity.addedOn = new Date();

 //Add a single space
 var STRING_SPACE = " ";
 entity.addedBy = STRING_SPACE;


};

 

Server

Entity – ListofContact

 

Code

        partial void listofContacts_Inserting(listofContact entity)
        {
            //when inserting, set added By to current windows user
            //If added By is still at default
            //entity.addedBy = entity.username;
            if (entity.addedBy == " ")
            {

                //If user is authenticated, then get username
                if (this.Application.User.IsAuthenticated)
                {

                    entity.addedBy = this.Application.User.Name;

                } // if (this.Application.User.IsAuthenticated)

            } // if (entity.addedBy == " ")

        }  // listofContacts_Inserting