I have read here that bind variables can be used in dynamic SOQL (which I am aware of) But on the code:
List<sObject> testQuery = Database.query('SELECT id from Account where Name = :a.Name');
It says that variable does not exist.
Though I know the workaround to put that in the string with the binding of the variable then pass in the whole string in the query.
Question is when does it became a "Bind Variable Field" and when does it became a "Bind Variable"
Bind variable: you have a local primitive data type variable and you want to bind its value. I.E.
Integer quantity = 10;
Database.query('SELECT AccountId FROM Asset WHERE Quantity =: quantity');
Bind variable fields: you have a complex object, like a custom type or a SObject, and you want to bind the value of its property. In this case you must declare a variabile of the correct primitive data type assinging the value you want to bind. I.E.
Account acc = ...;
String industry = acc.Industry;
Database.query('SELECT FirstName, LastName FROM Contact WHERE Account.Industry =: industry');
Keep in mind that the variable you want to bind must have a local scope.
Not Allowed:
Database.query('SELECT Id FROM Account WHERE Name =: SomeClass.SOME_CONSTANT');
Allowed:
String name = SomeClass.SOME_CONSTANT;
Database.query('SELECT Id FROM Account WHERE Name =: name');
:account.xyz__c you're trying to bind a field (xyz__c) of a variable (account).