2. Console App (Code-First)

Question 1

What’s the role of the DbContext class in EF?

Answer 1

It practically represents a database.

To connect to a database, we write a class that derives from DbContext. Each DbContext class we write gives us access to a specific database.

Question 2

What’s a DbSet in the context of EF?

Answer 2

Practically, a table in the database.

In DbContext, we can create properties that are type DbSet. The generic type parameter T will be an entity.

Question 3

How do you specify a connection string for a DbContext class?

Answer 3

By overriding OnConfiguring, which takes in a DbContextOptionsBuilder parameter that we can use to set the connection string to our DB.

Question 4

What NuGet package do you need to work with a PostgreSQL database on EF Core?

Answer 4

npsql.EntityFrameworkCore.PostgreSQL

Question 5

What NuGet package do you need to use EF Core tools?

Answer 5

Microsoft.EntityFrameworkCore.Tools

Question 6

How do you add migrations to a project using EF Core?

Answer 6

By running dotnet ef migrations add -p .

Question 7

How do you apply migrations to a database using EF Core?

Answer 7

By running dotnet ef database update -p .

Question 8

How do you create a database using EF Core code-first approach?

Answer 8

By creating a new class that derives from DbContext, configuring it by overriding the OnConfiguring base method which takes in a DbContextOptionsBuilder object for dependency injection, and then creating and running migrations.

Question 9

How do you create a table using EF Core code-first approach?

Answer 9

By creating a new class to be used as an entity, defining properties in it to be mapped to columns, and adding a new property to your DbContext child class with the type DbSet — T being the entity class type.

Question 10

How do you access a database table in code?

Answer 10

By instantiating a context class object and calling the DbSet property that corresponds to the table you’d like to access.

eg. 

var db = MyContexT();
var tb = db.MyTable; ~~~ ~~~

Question 11

How do you add a new record to the database in code?

Answer 11

By using a context object to access the table and call the Add method on it.

eg. 

var db = MyContexT();
db.MyTable.Add(new MyRecord {Name = "Foo"}); ~~~ ~~~

Question 12

After using a context object to write data to a database, what else must you do in order for those writes to actually be applied?

Answer 12

Use the context object to save changes.

eg. db.SaveChanges();