How to dynamically set values to object fields?

Question

I have and object 'Car__c' in a package with namespace 'car'. There is a field name 'Price__c' and a lookup field name 'Car_Segment__c'.

To initialize 'Car__c' and assign values to its fields from a class in 'car' package, I am doing something like -

Car__c carobj = new Car__c();
carobj.Price__c = 1000000;
carobj.Car_Segment__c = '0034R00003bVDo1QAG'; // id assignment in this way is for illustration purpose only

There is another package with namespace 'tyre' having an object 'Tyre__c'.

Now I have extended the 'Car__c' object in the other package with namespace 'tyre' by adding an object 'car__Car__c there. There is a requirement to add a lookup to object 'Tyre__c' so I have also added it as a field in my extended object with referenceTo value as -

<referenceTo> tyre__Tyre__c </referenceTo>

I want to assign values to this field too. I am doing something like -

    Car__c carobj = new Car__c();
    carobj.Price__c = 1000000;
    carobj.Car_Segment__c = '0034R00003bVDo1QAG';
    
    //need to check whether the lookup field exists before assigning values
    SObject so = Schema.getGlobalDescribe().get('Car__c').newSObject();
    if (so.getSobjectType().getDescribe().fields.getMap().containsKey('tyre__Tyre__c')) {
       carobj.put('tyre__Tyre__c', '1034R08603bVDo1QAc');
    }
   insert carobj;

In the second scnario, is this the correct way to initialize the object and assign the values ? If not then can you please suggest a correct and efficient way ?

Answer 1

Using newInstance is kind of redundant because you don't use created SObject instance.

Here are a few options which you can use

I think this one is the best option:

Car__c carobj = new Car__c();
carobj.Price__c = 1000000;
carobj.Car_Segment__c = '0034R00003bVDo1QAG';

//need to check whether the lookup field exists before assigning values

String fieldName = 'tyre__Tyre__c';
SObjectField field = Car__c.fields.getMap().get(fieldName);
if (field != null) {
    carobj.put(field, '1034R08603bVDo1QAc');
}
insert carobj;

Here is another option if you want something more dynamic

    Car__c carobj = new Car__c();
    carobj.Price__c = 1000000;
    carobj.Car_Segment__c = '0034R00003bVDo1QAG';
    
    //need to check whether the lookup field exists before assigning values
    if (Schema.getGlobalDescribe().get('Car__c').getDescribe().fields.getMap().containsKey('tyre__Tyre__c')) {
       carobj.put('tyre__Tyre__c', '1034R08603bVDo1QAc');
    }
   insert carobj;