Part II (closed)

Question 1

How can EF react when adding multiple objects and an error occurs?

Answer 1

On saving changes EF detects that the bad insert item is not inserted and tries to add it once again and throws an error. A solution is to create a new dbcontect (brute force) or mark the bad item state as detached. In case of changed items (updated or deleted) state should be changed to unchanged.

Question 2

How to you SaveChanges in EF in context of adding items?

Answer 2

When considering only a few inserts SaveChanges can be invoked after every insert, when bulk only once.

Question 3

Why is maximum request length defined in ASP.NET?

Answer 3

To avoid DoS (Denial of Service) attack.

Question 4

How is relationship many-to-many called when the joining table has additional data?

Answer 4

Many-to-many join with payload.

Question 5

What is a database sharding?

Answer 5

A way of splitting databases and improving performance. Similar to horizontal partitioning but instances can exist independently (smaller tables are duplicated).

Question 6

Horizontal partitioning vs vertical partitioning?

Answer 6

Horizontal is dividing data while vertical is dividing schema.

Question 7

What is an N+1 problem?

Answer 7

A problem in which in a relationship 1-to-many (e.g. car and wheels) we want to get for a set of items all its children then N+1 queries can be generated, to avoid this we can load all children to memory and then join it. In EF it can be solved by eager loading using Include.

Question 8

SOAP vs REST?

Answer 8

REST is simpler, without contract, should be controlled by HATEOAS, no backup for security, uses HTTP POST, GET, DEL, PUT, different formats

SOAP is heavier, it serves WS-Security, WS-ReliableMessaging, WS-AtomicTransaction, provides contract, uses HTTP POST, only XML

Question 9

What is Liskov substitution principle?

Answer 9

That classes derived from abstractions should be used everywhere where abstraction without affecting application. For example Store, StandardMessageStore and RotatingStore which deletes some messages. Then getMessages won’t retrieve all messages.

Question 10

Compare Inversion of Control, Dependency Inversion and Dependency Injection?

Answer 10

Inversion of control, inverts program flows because custom code is called by some framework, Dependency Injection helps IoC achieve this goal. Dependency Inversion is about references -> high level module and low level modules should depend on abstractions.

Question 11

Compare Read Committed, Repeatable Read and Serializable?

Answer 11

RC ensures that all data is committed, future read can bring different results, RR guarantees that future reads will show exactly the same data while SR guarantees that no new data is inserted.

Question 12

Main ways of structuring view model and model in ASP.NET MVC?

Answer 12

Inheritance, composition, duplication of code.

Question 13

What’s the convention for naming partial views in ASP.NET?

Answer 13

To start with underscore _ and suffix with “Partial”

Question 14

What data models are there in EF?

Answer 14

Conceptual, logical, physical.

Question 15

Main approaches to data in EF?

Answer 15

Model-first (designer generates DB and domain classes), database-first (designer, generates domain classes), code-first (code, migrations).

Question 16

What object hold all the information required to query database and map to entity objects and what are its main parts?

Answer 16

EDM (Entity Data Model) which is created in memory holds:

• conceptual model: domain classes, context class, configuration
• storage model: information about db schema
• mappings: mapping between conceptual and storage

Question 17

What is the Object Service in EF?

Answer 17

A part of EF responsible for talking with database, especially materializing queries (converting query’s result to entity objects.

Question 18

What is Entity Client Data Provider in EF?

Answer 18

A part of EC responsible for transalting LINQ to Entities query or Entity Sql Query to SQL.

Question 19

What represents a session with the underlying database in EF?

Answer 19

DbContext

Question 20

What is an entity in EF, what are type of entity’s properties?

Answer 20

A class that can be used with DbSet and relates to single table in a database. Its properties reference columns of this table. There are two types of entities properties:

• Scalar Property (single value, column)
• Navigation Property:
  
  • Reference Property,
  • CollectionProperty

Question 21

What is a POCO class?

Answer 21

Plain Old CLR Object - a class that doesn’t contain any framework-specific elements, doesn’t derive from any specific base class.

Question 22

What are 2 types of entities in EF?

Answer 22

POCO, POCO Proxy (dynamic proxy) which enables lazy loading, but POCO class must fullfil some requirements .

Question 23

Which state conversion is handled automatically by EF context?

Answer 23

From Unchanged to Modified.

Question 24

What are persistence scenarios in EF?

Answer 24

Connected, disconnected

Question 25

What is OCC (Optimistic Concurrency Control)?

Answer 25

A way of maintaining concurrency in which there are no locks but each transaction does its work but before commiting it checks if another transaction made any changes. If yes it restarts itself and tries again. Good for low data contention systems. Pessimistic concurrency relates to locking methods.

Question 26

How to improve performance in EF while getting read-only properties?

Answer 26

Use AsNoTracking on DbSet.

Question 27

What kind of joining table is supported in EF without the need for creating additional model class and managing it?

Answer 27

Joining table without payload.

Question 28

How to retrieve in SQL number of rows affected by last statement?

Answer 28

Using @@ROWCOUNT

Question 29

Compare Data Driven Dev with Domain Driven Dev?

Answer 29

In DDD you should first create domain model without database. The best way is to create it without database, use TDD and create an application. Only then you should create a database but using the repository pattern to introduce abstraction.

In Data Driven Dev you first create your database and your model reflects that database and operations on it -> CRUD.