What is a dynamic apex in salesforce? - salesforce

Question

I am in the learning stages of Salesforce Apex. I have read the topic of Dynamic Apex and was not able to understand the concept. Can someone explain it how to deal with it and in which scenarios it is best to use?
Thanks in advance.

Answer 1

Use case 1:
You are developing a page that reads the salesforce object meta data to display the object records to the user. You want to use the describe global methods but you dont know how to combine standard SOQL with the generic SObject type.
Standard SOQL eg
Person__c [] persons = [SELECT Id, Name, Age__c, Height__c FROM Person__c];
But the describe global metadata methods returns a SObject types.
Solution:
Use the describe global methods to get a list of objects, then further get all the fields on that object. Build a SELECT statement in a local string variable with all the fields then execute the query with Database.query().
string objectfullname = 'scenario__c';
Schema.SObjectType targetType = Schema.getGlobalDescribe().get('scenario__c');
if (targetType == null) {
system.debug('Type not found: '+objectFullname);
throw new TypeNotFoundException(objectFullName);
}
Schema.DescribeSObjectResult typedescription = targetType.getDescribe();
Map<String, schema.Sobjectfield> resultMap = typedescription.Fields.getMap();
string query = 'SELECT ' + string.join(new List<string>(resultMap.keySet()), ',') + ' FROM '+ objectfullname + ' LIMIT 100';
sobject [] records = Database.query(query);
Use Case 2
You want to loosely couple your code with custom objects in a beta managed packaged so that the managed packaged can be uninstalled and upgraded.
Solution
When you use the Database.query() method, your code is not compiled against the custom object so it can be re-installed without any need for commenting out code to remove the dependency.
Use Case 3
You have a trigger that copies records to another custom object after insert according to an dynamic field mapping schema. You can't code it in the standard way [SELECT ...] because you only know what object you are inserting to at run time.
Solution
Again, use describe global methods & Database.query to get the records and type information then you can insert into the target object like normal DML.
sobject newRecord = ...
for (integer i = 0; i < fieldCount; i++) {
newRecord.put(fields[i],values[i]);
}
insert newRecord;
If you are doing bulk inserts, like always, make sure that you dont put DML (insert, update) statements in a loop.