Get a value from SOQL query into string

Question

Quick Question, I have an soql query that looks like this:

List<Service_Instance__c> Servic = [Select Account__c, Account_Customer_Account_Number__c, Airports__c, Local_Service__c, Location__c, Terminal__c, Physical_ID__c
         from Service_Instance__c where USI__c =:usi1 limit 1];

I want to assign Account_Customer_Account_Number__c to a string for the next query I tried the following :

  AccNum = [Select Account_Customer_Account_Number__c
         from Service_Instance__c where USI__c =:usi1 limit 1];

and

  AccNum = Servic[0].Account_Customer_Account_Number__c;

I've also tried to change the AccNum from String to Integer to decimal and nothing worked.
I want to sort this out in order for this query to work :

 List<Account> AccName = [Select Name, Customer_Account_Number__c 
         from Account where Customer_Account_Number__c =:AccNum limit 1];

Answer 1

Viewing your code I will asume that you have declared AccNum as string (you should say it for better help)

if that is the case and viewing your error line, try to change this:

AccNum = Servic[0].Account_Customer_Account_Number__c;

for this:

AccNum = string.valueOf(Servic[0].Account_Customer_Account_Number__c);

Answer 2

Try this,

String AccNum = [Select Account_Customer_Account_Number__c
         from Service_Instance__c where USI__c =:usi1 limit 1].Account_Customer_Account_Number__c;

Answer 3

Assuming that the Account__c field is a look-up to the account that you are trying to reference in your second query, I'd say the best approach is to query those fields directly in the first query:

List<Service_Instance__c> Servic = [
    SELECT Account__c, Account__r.Name, Account__r.Customer_AccountNumber__c, Account_Customer_Account_Number__c, Airports__c, Local_Service__c, Location__c, Terminal__c, Physical_ID__c
    FROM Service_Instance__c 
    WHERE USI__c =:usi1 limit 1
];

for (Service_Instance__c si : Servic){
    system.debug(si);
    system.debug(si.Account__r.Name);
}