Apex regex to validate the Salesforce dot notation

Question

In Apex we can access a field using the dot notation

Example : Owner.Name

I am looking for a regex to validate that notation

I come up we the regex below

String validateDotNotation='([a-zA-Z]([a-zA-Z1-9]|[a-zA-Z1-9]_[a-zA-Z1-9])*[a-zA-Z1-9](__[rRcC])?\\.)*([a-zA-Z]([a-zA-Z1-9]|[a-zA-Z1-9]_[a-zA-Z1-9])*[a-zA-Z1-9](__[cC])?)'

Some explanations

[a-zA-Z] : validate the first char must be alphabetic upper or lower case
[a-zA-Z1-9] : validate char must be alphanumeric 
[a-zA-Z1-9]_[a-zA-Z1-9] : validate _ must not be two consecutive _
[a-zA-Z1-9]|[a-zA-Z1-9]_[a-zA-Z1-9] : validate middle field name chars can be alphanumeric & non consecutive _
[a-zA-Z]([a-zA-Z1-9]|[a-zA-Z1-9]_[a-zA-Z1-9])*[a-zA-Z1-9] : validate a field name
(__[rRcC])? : custom or relationship field ending 
(__[cC])? : custom field ending

Salesforce naming rules for a field API Name

Can you tell me if it's correct or if there is a better way to do it ?

Answer 1

"Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems."

-Jamie Zawinski

Regular expressions do have their uses, but I find myself trying to avoid using regex if I can.

I think there's a better solution in your case.

Using Apex, you can pull the fields from an object (any sObject).

Map<String, Schema.SObjectField> M = Schema.SObjectType.Account.fields.getMap();

Using this approach, you can do something that your regex will never be able to, you can verify that the given field name is actually a field on your target object. Given the line of code above, and assuming you have a variable called fieldName...

if(!M.keySet().containsKey(fieldName)){
    // add an error to be displayed on your Visualforce page here
}

It gets a bit more involved if you want to do this for related fields, but using String.split('.'), Schema.getGlobalDescribe(), and Schema.DescribeFieldResult.getReferenceTo(), would accomplish what you're looking to do here.

Answer 2

Field validation

/^[a-zA-Z][a-zA-Z0-9]*(_[a-zA-Z0-9]+)*(__[cC])?$/

Reference validation

/^[a-zA-Z][a-zA-Z0-9]*(_[a-zA-Z0-9]+)*(__[rRcC])?$/

Explanation

[a-zA-Z] : Validate the first char must be alphabetic upper or lower case
[a-zA-Z0-9]* : Following the first char can be any amount of alphanumeric characters
(_[a-zA-Z0-9]+)* : If we have an underscore must be followed by at least one alphanumeric character
(__[rRcC])? : custom or relationship field ending optional (? = matches none or one time)
(__[cC])? : custom field ending (? = matches none or one time)

The issue with your expression

String validateDotNotation='([a-zA-Z]([a-zA-Z1-9]|[a-zA-Z1-9]_[a-zA-Z1-9])*[a-zA-Z1-9](__[rRcC])?\\.)*([a-zA-Z]([a-zA-Z1-9]|[a-zA-Z1-9]_[a-zA-Z1-9])*[a-zA-Z1-9](__[cC])?)'

Is that you can't have only one char before the first char, like a_b__c, or a__c. And can't have only a char at the end following an underscore like hello_f__c And that you are leaving 0 out with 1-9