.Net EF Core

Question 1

How to migrate database changes from EF core to database?

Answer 1

Using database migrations , by running commands or by calling migrate method in startup of the application

Question 2

What happens when you write filtering , sorting , paging before execute command?

Answer 2

The query runs inside DB instead of in code which improves the performance of query

Question 3

What are the two types of queries ?

Answer 3

1. Normal, read-write query
   2.AsNoTracking, read-only query

Question 4

What are different types of loading data?

Answer 4

Eager loading, Explicit loading, Select loading, Lazy loading

Question 5

Will EFCore load relationships by default?

Answer 5

No , it will not . By default , they will be null

Question 6

What is Eager loading?

Answer 6

Eager loading is when you query one type of entity and immediately load related entities as part of it. Eager loading is specified via two fluent methods , Include and thenInclude

Question 7

What is the issue with eager loading?

Answer 7

If you do not specify .Include() , no related entities are loaded or only partial set may be loaded if previously some related entities are loaded

Question 8

What is the advantage of eager loading?

Answer 8

Loads all the data of the related entity using minimum database round trips

Question 9

What is the disadvantage of eager loading?

Answer 9

Since it loads all the data of the related entity , in some cases you might do not want to load all of the columns

Question 10

What are the linq methods you can add in your Include() methods?

Answer 10

Where, OrderBy, OrderByDescending, ThenBy, ThenByDescending, Skip and Take

Question 11

What is explicit loading?

Answer 11

After loading primary entity class , you can explicitly load any other relationships using Load() method

Question 12

What is the issue with explicit loading?

Answer 12

A seperate db query is run each time you call load() . So if you were to load table of N records then N+1 queries need to be processed instead of just one query in case of eager loading

Question 13

What is the disadvantage of explicit loading?

Answer 13

More database round trips compared to eager loading. If you know upfront that you need related entities use eager loading as it takes fewer round trips . On the other hand you know you need to load related entities for fewer instances use explicit loading

Question 14

What is select loading?

Answer 14

Use the select linq method to select few standard properties from entity and its related entity.

Question 15

What is advantage of select loading?

Answer 15

Only the required properties are loaded

Question 16

What is the disadvantage of select loading?

Answer 16

Need to explicity specify the needed properties

Question 17

What is Lazy Loading?

Answer 17

With lazy loading , navigational properties are loaded automatically only when needed . It has the same cost that of explict loading

Question 18

How to setup lazy loading?

Answer 18

It can be setup by adding proxies library when configuring db context - locks you into setting up lazy loading for all relationships . Second option is by injecting a lazy loading method into the entity class via its constructor by DI

Question 19

How to configure simple loading through dbcontext?

Answer 19

Add keyword virtual before all properties and add method UseLazyLoadingProxies when setting up uour dbcontext

Question 20

How lazy loading works?

Answer 20

Since you have configured lazy laoding in entity classes and in the way you create the dbcontext, reading relationships is simple. You don’t need extra Include method in your query because data is loaded from db when your code access that relationship property

Question 21

What is client vs server evaluation feature?

Answer 21

This feature gives you the oppartunity to adapt/change the data within the last part of the query, which can save you from having to apply an extra step after the query

Question 22

Can you use any LINQ command on client vs server evaluation property?

Answer 22

No , an InvalidOperationException is returned with message - could not be translated

Question 23

What is Iqueryable<T> type?</T>

Answer 23

If you want use sort , filtering and paging on a Type , it should implement IQueryable

Question 24

What is State property ?

Answer 24

Every entity class instance has State property which tells EF core what to do with this instance when savechanges is called . Possible values for state are Added, Unchanged, Modified, Deleted, Detached

Question 25

When does entity instance get tracked?

Answer 25

When they are read without using .asnotracking() or after an entity instance has been used as a parameter to EF Core methods(such as Add, Update or Delete), it becomes tracked

Question 26

What happens when the savechanges method is called?

Answer 26

EF core runs a method called Detect Changes, which compares the tracking snapshot against the entity class instance that it handed to the application when query was originally executed

Question 27

What is a disconnected update?

Answer 27

In this , there are two different instances of application’s DbContext.For example , In web applications ecah HTTP request is typically new request, with no data held feom last HTTP Request

Question 28

What are the two main ways of handling disconnected updates?

Answer 28

1.You send only the data uou need to update back from the first stage.
2.you send all the entity data to re-create the entity calss back from first stage

Question 29

What does update command do?

Answer 29

It replaces all the row data-updates all columns for the given primary key

Question 30

What is principal entity?

Answer 30

Contains a primary key that dependent relationship refer to via a foreign key

Question 31

What is Dependent Entity?

Answer 31

Contains a foreign key that refers to principal entity’s primary key

Question 32

Can the dependent entity exist without principal entity?

Answer 32

If the primary key of principal entity is nullable in dependent entity . Then even if you delete the principal entity, dependent entity remains unaffected

Question 33

What is connected state update?

Answer 33

It assumes that same context is used for both the read and the update