Part III

Question 1

How to turn off lazy loading for navigation property in EF?

Answer 1

By not making it virtual.

Question 2

How to save changes to whole entity graph in EF?

Answer 2

Compare objects keys to default ones. If default then Context.Entry(object).State is Added else Modified.

Question 3

How to improve performance of inserting, removing collections in EF?

Answer 3

By using DbSet.AddRange, InsertRange.

Question 4

How to handle concurrency in EF with rowversion and DB-first?

Answer 4

Add new column of type rowversion (8 bytes incremented number for whole database). In EF diagram set properties of this column concurrency to fixed. Then all update will dheck it.

Question 5

What’s the information expert principle?

Answer 5

It states that responsibility should be given to a class which contains all the information to handle it i.e. look at the classes and decide.

Question 6

What are 2 main purposes of controller in GRASP?

Answer 6

To execute a system operation (adding user, adding item to cart), second is providing a layer between UI and domain models.

Question 7

What flexibility give us the controller in GRASP?

Answer 7

We can change user interface without changing the logic - e.g. change web to terminal.

Question 8

What are some points to favor composition over inhertiance?

Answer 8

Composition gives you runtime execution. Possible smaller number of classes.

Question 9

What is indirection in GRASP?

Answer 9

A principle that states that interaction between objects is done via intermediate object to preserve low coupling (e.g. introducing Configuration class not providing config values directly in clients).

Question 10

What’s the association, composition and aggregation? How to draw them in UML?

Answer 10

Association states that classes uses each other somehow. Composition is a relationship in which child cannot exist without parent (house and room), and in aggregation it can exist independently (car and engine). Composition - filled diamond (by parent), aggregation - empty diamond, association - straight line, may have arrows

Question 11

What are the main parts of state pattern?

Answer 11

Context and state.

Question 12

What is covariance?

Answer 12

Returning or assigning more derived types than declared.

Question 13

What is contravariance?

Answer 13

Assinging or providing parameters of less generic types than declared.

Question 14

What’s the difference between tier and layer?

Answer 14

Layer is logical, tier is physical.

Question 15

What are the parts of 3-tier application?

Answer 15

Presentation, application and data.

Question 16

What are main layers of application?

Answer 16

Presentation, application, business logic, data.

Question 17

Rules for lazy loading in EF?

Answer 17

In cofiguration: LazyLoadingEnable, ProxyCreationEnabled and particular property should be public virtual

Question 18

What’s the concurrency model in EF? How to handle it (example).

Answer 18

Optimistic concurrency. A row of type rowversion (timestamp) must be added to tables. It’s incremented each time an operation is done on a row. Then in database designer select this column and set concurrency as fixed. Only then exception about concurrency wil be thrown.

Question 19

How is .NET Core lifecycle different from .NET Framework?

Answer 19

.NET Core is also build using MsBuild. It is then executed by CoreCRL (on different OS-es) which uses JiT compiler. The process is hosted using dotnet.exe process (it hosts CoreCRL and code) .NET Core can also be prebuilt to native code using AoT.

Question 20

What is AoT?

Answer 20

Ahead of Time compiler which compiles (currently only UWP). Compiler is called .NET Native. It produces package of native code that is then executed by CoreCRL.

Question 21

How many CLR instances are there in Windows for .NET Framework?

Answer 21

Separate instance for each .NET process.

Question 22

How is Xamarin app built?

Answer 22

First MsBuild then Xamarin Compiler which generates IL for Android (dll, exe) which is then executed by Mono Runtime (similar to .NET Core). On IoS Xamarin Compiler generates native code using AOT (ARM language).

Question 23

How fody works?

Answer 23

It’s IL weaving. It has a MsBuild post build action which modified IL generated code.

Question 24

What is weaving? What types of weaving are there?

Answer 24

Weaving is adding some additional code to application. It can be done to a source code or to IL code.

Question 25

Is it possible to add own mechanism for insertion, deletion and update of entity in EF?

Answer 25

Yes, by using stored procedures. Create procedure for each CUD operation and then in diagram set that this entity operations are connected to those procedures. Then while modifying instances of the entity and saving changes those procedures will be invoked.

Question 26

What is DbEntityEntry used for?

Answer 26

It can be used for retrieving information about tracked entity. It contains information about changed values and current entity state. It also enables to set entity's state.

Question 27

How is table-valued function different from stored procedure? What does it enable in EF?

Answer 27

It's composable. In EF it enables to use table-valued function in Linq To Entities.

Question 28

How can you validate entities in EF?

Answer 28

You can override validation method in DbContext. Then e.g. while saving changes an error can occur due to this validation.

Question 29

How can you control transactions in EF? What's the behavior of SaveChanges in such a situation?

Answer 29

By using BeginTransaction or UseTransaction. SaveChanges doesn't immediately commit transactions,explicit call to transaction.Commit is required.

Question 30

How Just My Code works?

Answer 30

It looks for optimized assemblies or that without pdb files and steps over them while debugging.