Hi all.

I'm writing my first trigger on SalesForce.

The goal would be: determine the value of a proposal (Proposal__c) updating its field called Proposal_Value__c (Currency), getting the sum of Item_Value__c(currency) that resides in a Proposal child object.

The trigger should be called inserting, updating or deleting a proposal Line_Item

trigger updateProposal on Proposal_Line__c (after delete, after insert, after update) {
	
	Double proposalValue = Proposal__c.Proposal_Value__c;
	
	List proposalLines =
	[SELECT  j.Proposal_Line_Value__c FROM Proposal_Child__c j FOR UPDATE];
	
	for (Proposal_Child__c pl: proposalLines) {
		
		proposalValue += pl.Proposal_Line_Value__c;	
    }
    update proposalValue ;
}

I have an error declaring proposalValue (the first variable): Illegal assignment from Schema.SObjectField to Double

I've also checked in the schema explorer that says this variable is of Double type.

Thanks for any suggestion.