Does impacting other instances mean that if we write a code for creating an account, the account will be created in all the instances of Salesforce that is in use across the globe?
There is a difference between Instance & Org. Instance means naXX, the server your Salesforce instance (e.g. https://na35.salesforce.com) is running however multiple Orgs will be operated on the same instance. For eg: there are two orgs, X and Y both are on na35 instance, if we create an Account in Org X, it will be only stored in X not in Y.
When does the need for a APEX code arise? Is it just experience that will teach us that a particular solution is not possible without an apex code? how is this different from a VF code?
Sometimes we come across such complex scenarios which can not be fulfilled by standard sales force configuration. Scenarios like: Schedule a record creation or updation, Complex Calculation of Revenues on Account.
For e.g. when you save a new record or update a record, you want to do something which is not possible using Standard Salesforce Configuration, e.g. though workflow, flow or process builder, then we have to write APEX. We can write APEX for existing Standard object or custom object we created.
If we want to create a completely new user interface screen for any standard object or custom object, we create VF Pages. VF pages do not need APEX, if we can use Standard Controller. We will need write APEX custom controller to do complex things on VF Pages. You can read more about Standard & Custom Controller.
What will happen if you deleting a parent record which is a standard object and lookup from a custom object. e.g. Travel Request has a lookup field to Contact.
You can select either of below mentioned options while creating a lookup:
· Clear the value of this field – Default option
· Don’t allow deletion of the lookup record that’s part of a lookup relationship
· Delete this record also: This new option cascades the deletion of a referenced lookup record to dependent records. It is available only for lookup fields in a custom object; however, the lookup field can reference either a standard or custom object. Choose this option for tightly-coupled record relationships when you want to completely delete related data in one operation.