sql joins/abstract/interface/entity

Question 1

SQL Joins

Answer 1

• Inner Join – returns rows with matching values on both tables
• Left/Right Join – returns all rows of either side and also matching values from other side
• Outer Join – returns all rows from both left and right side and puts nulls where there are no matches
• Cross Join – combination of all rows of both tables
• Self Join – joining self table

Question 2

SQL Tables - migrating data

Answer 2

• SSMS tool (Export/Import Wizard) – takes care of exporting and importing process
• SQL script – queries to move data
• Backup/restore – create backup of db and restore it on next db server

Question 3

Abstract class

Answer 3

• Blueprint for other classes
• Good for when you need a common base with some shared implementation among derived classes
• Allows for code reuse

Question 4

Interface

Answer 4

• Good for when you know methods need to exist but you also know they may need to be implemented differently
• If you want to change the interface like adding new method / property to it, it will break all implementations
• Cannot have access modifiers
• Cannot have constructor
• Can only define methods
• You implement an interface (you inherit an abstract class)
• Composition
• Multiple unrelated classes can implement
• Allowing a class to implement multiple interfaces

Question 5

Scoping

Answer 5

o Public – any class has access
o Protected – inherited class has access
o Private – only same class has access
* Interface – public
* Abstract class – private, protected, public

Question 6

Entity Framework

Answer 6

ORM (Object Relational Mapper) framework
* Makes it easier to work with databases using C# objects
* Abstracts away underlying database interactions
Key components
* DbContext – represents a session with the database
o Manages database connections, transactions
o Provides set of APIs for querying and interacting with data
* DbSet – represents a table
Provides a collection of entities
* Entities – represents objects that represent database records
o C# classes that represent objects in database
o Class properties == database columns
Best practices
* Managing lifespan of connection of DbContext

Question 7

Authentication vs authorization

Answer 7

 Authentication – verifying user login credentials
 Authorization – verifying user permissions