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I have a Droplist for Approvers and the DataSource of Droplist to /SharedData/Approvers.

I don't want the current user to have his own name in the list.
For example, DataSource List is having A, B and C

When A logs in, it should show B and C but not A. Or it should be validated when A selects himself as Approver.

Any idea?

It is possible via both a custom field implementation or field validation. Below is the code for both ways.

Solution 1 - A Custom Validation

You should implement a class which will extend the StandardValidator. The code snippet is provided below to create a custom validation for the droplist.

[Serializable]
public class UserValidation : StandardValidator

 protected override ValidatorResult Evaluate()
 
 var selectedValue = ControlValidationValue;

 var username = Context.User.LocalName;

 if (!selectedValue.IsNullOrEmpty() && selectedValue.Equals(username))
 
 Text = GetText($"Field GetFieldDisplayName() cannot select your own name");
 return ValidatorResult.FatalError;
 

 return ValidatorResult.Valid;
 

 protected override ValidatorResult GetMaxValidatorResult()
 
 return GetFailedResult(ValidatorResult.Error);
 

 public override string Name => "User Validator";

In the code above, I have use the LocalName property. This property will return me only the name. Example, Admin.

Note that this piece of code will validate the username against the item name. It is feasible check the username against a field on the items from the list but it will require additional code to retrieve the selected item then read the field.

Once you have deployed the above code, you will need to create a new validation item under the path /sitecore/system/Settings/Validation Rules/Field Rules.

Change the Type to match your namespace. Also, you need to assign the newly created validation rule to the field.

Solution 2 - A Custom Field

You can implement a custom droplist which extend the ValueLookupEx from the namespace Sitecore.Shell.Applications.ContentEditor in the Sitecore.Kernel.dll. The purpose will be to remove the current user from the list of items if it matches.

public class CustomDroplist : ValueLookupEx

 protected override Item[] GetItems(Item current)
 
 var items = base.GetItems(current);

 var username = Sitecore.Context.User.LocalName;

 var resultItems = items.Where(w => !w.Name.Equals(username)).ToArray();

 return resultItems;
 

Once implemented, deploy the code and load the content editor. Then, switch the database to core and navigate to the path /sitecore/system/Field types/List Types and create a new field using the template Template field type.

Update the assembly and class with yours.

Outcome