With sharing and Without sharing in salesforce

Today we will try to cover the topic "With sharing and Without sharing in Salesforce".

With sharing:

We use the keyword "with sharing" before declaring class so as to take into account the sharing rules for the user. By default apex class runs into system mode so as to avoid code failure because of permissions.

Syntax:

Without sharing:

Sharing rules are not taken into account for the user.

Syntax:

POINTS TO NOTE:

1. If we do not declare class with "With sharing" or "Without sharing" the class will not take into account the sharing rules but if this class is called from another class which is declared with "with sharing" it will take into account the sharing rules.
2. If the class with "with sharing" is calling method of another class with "without sharing" than the method inside "without sharing" class will execute without sharing rules.
3. If the class with "without sharing" is calling method of another class with "with sharing" than the method inside "with sharing" class will execute with sharing rules.
4. Inner class do not have sharing settings of parent class.
5. Class have sharing settings of parent class when we implements it or extends it from parent class.

Now, Let us go through below scenarios for better understanding.

1) Let say user do not have permission on a child object and he is having permission on parent object to read/create/edit/delete parent object, If I create a trigger on parent object to insert a child record after parent record is created, will it create a child record or not after user insert parent record manually?

It will create a child record (Trigger/apex class runs in system mode).

2) If in the above scenario from trigger let say I am calling apex class which is in "with sharing" mode and where I am inserting child record after parent is inserted manually by user, so will it create a child record?

It will create a child record.(with sharing keyword has nothing to do with user permissions it only takes into account the sharing rules for the user).

3) Let say if my apex class which is not declared with any keyword "with sharing" or "without sharing" is fetching opportunity records and the user with which this class is running does not hold any opportunity records or no opportunity record is shared with user, in this case the class will be able to fetch opportunity records since the apex class runs in system mode though the user have CRUD permissions or does not have CRUD permissions on opportunity.

4) Let say if my apex class is declared with "with Sharing" keyword and is fetching opportunity records and the user with which this class is running does not hold any opportunity records or no opportunity record is shared with user, in this case the class will not be able to fetch opportunity records though the user have CRUD permissions or does not have CRUD permissions on opportunity.