Apex errors with Custom button to add existing records on a custom object

Question

I am receiving apex errors with the following code:

public with sharing class AddExistingSpecsExt {

    public Specifications__c loadedSpec { get; private set; }

public AddExistingSpecsExt() {
    String specId = ApexPages.currentPage().getParameters().get('id');
    if (String.isBlank(specId)) return;

    List<Specifications__c> candidates = [
        SELECT Id, Name, Product__c FROM Specifications__c WHERE Id = :specId LIMIT 1
    ];
    if (!candidates.isEmpty()) loadedSpec = candidates[0];
}
    public PageReference associate () {

        Specifications__c candidates = new Specifications__c ( Id = Specifications__c.Product__c, Name = Specifications__c.Id);

        try {
            Database.update(candidates);
        } catch (Exception error) {
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, 'Error while associating.' + error.getMessage()));
        }

        PageReference page = new PageReference('/' + candidates);

        return page.setRedirect(true);
    }

    public PageReference cancel () {
        PageReference page = new PageReference('/' + Null);
        return page.setRedirect(true);        
    }

}

Attempting to add records to a related list through a custom button and small vf page.

The Error is Line 16

Invalid initial expression type for field Specifications__c.Id, expecting: Id

Any help?

Answer 1

You are confusing data and metadata. So instead of getting a value, you are getting SObjectField.

Id data = loadedSpec.Id;
SObjectField metadata = Spefications__c.Id;

You need to use the former (data) in your code:

Schema.SObjectField idMetadata = Specifications__c.Id; // you don't need this
Id idData = loadedSpec.Id;

SObjectField productMetadata = Specifications__c.Product__c; // you don't need this
String productData = loadedSpec.Product__c;

Specifications__c record = new Specifications__c(Id=idData, Name=productData);

Also, you don't even need to instantiate a new Specifications__c record at all. Just do:

loadedSpec.Name = loadedSpec.Product__c;
//update logic

One last note, you should return null in your catch block after calling ApexPages.addMessage.

Answer 2

I wonder why you are assigning the ID into a Name field and a lookup (I assume it's a lookup) into the ID field.... but that could be the correct logic...

Specifications__c candidates = new Specifications__c ( Id = Specifications__c.Product__c, Name = Specifications__c.Id);

If Product__c is not an ID field, you will get an error.