What does "Illegal assignment from Schema.SObjectField to String" mean?

Question

I wrote the following trigger and I'm getting the error :

Illegal assignment from Schema.SObjectField to String

But I don't know how to fix it. I wrote a similar trigger before and didn't have any issues.

trigger AccountDuplicates on Account (before insert, before update) { 
for (Account myaccount : Trigger.new) {
        List <Account> dupes = [SELECT Name FROM Account WHERE Name = :(myaccount.Name)]; 
        if (dupes.size() > 0) { 
          myaccount.Duplicate_Account__c = Account.name;
        }
    }
}

The purpose of the trigger - when a new account is created that matches the name of an existing account, put the existing account's name into the "Duplicate Account" field.

Answer 1

The root problem is the line

 myaccount.Duplicate_Account__c = Account.name;

This references Account (the Schema sobject), not myAccount, the loop variable. Thus you need the following

trigger AccountDuplicates on Account (before insert, before update) { 
  for (Account myaccount : Trigger.new) {
    List <Account> dupes = [SELECT Name FROM Account WHERE Name = :(myaccount.Name)]; 
    if (dupes.size() > 0) { 
      myaccount.Duplicate_Account__c = myAccount.name;  // myAccount - the trigger loop vbl
    }
  }
}

Now, as @barcotter, said, you need to bulkify the trigger as SOQL inside of for loops is a no-no -- when the batch size is >100 as it can easily be in dataloader use cases, the governor limit on SOQL (100) will be exceeded.

I'll leave that as an exercise for you - there are many many resources (Google) on bulkifying triggers

Answer 2

See @crop1645 for the answer as to why your current code isn't working. But there is a larger issue here with bulkified code. See the example below that will only do one SOQL query no matter how many Accounts are inserted or updated.

trigger AccountDuplicates on Account (before insert, before update) { 

    List<String> names = new List<String>();
    for (Account a : Trigger.new) {
            names.add(a.Name);
    }

    Map<String, Account> duplicateMap = new MapMap<String, Account>();
    for (Account dup : [SELECT Name, Id FROM Account WHERE Name in :names]) {
        duplicateMap.put(dup.Name, dup); // Last duplicate found is stored in the map
    }

    for (Account a : Trigger.new) {
        Account dup = duplicateMap.get(a.Name);
        if (dup != null) {
            a.Duplicate_Account__c = dup;
        }     
    }
}

Answer 3

List<Account> dupes should be there instead of just List dupes . And moreover is the field " Duplicate Account" a text field or a lookup? If its a lookup , name cannot be assigned to it?