ORM/LINQ/SQL syntax

Question 1

What is ORM?

Answer 1

Object Relational Mapper

Question 2

what do ORMs do?

Answer 2

ORMs maps data from DB to an object in your program

Question 3

what are the two ways to connect your database to your code?

Answer 3

DB first and Code first

Question 4

what is DB first?

Answer 4

The DB structure already exists, classes are created based on the existing structure

Question 5

what is code first?

Answer 5

You create the DB structure based on the classes in the code

Question 6

A _____ instance represents a session with the database and can be used to query and save instances of your entities

Answer 6

DBContext

Question 7

Used to connect to your db

Answer 7

Connection String

Question 8

The project that you build and run

Answer 8

Startup project

Question 9

what is the syntax to create a migrations folder

Answer 9

dotnet ef migrations add -c –startup-project

Question 10

a snapshot of the database schema given the current state of your models

Answer 10

Migration

Question 11

what is the syntax to apply the changes of the latest migration to your database

Answer 11

dotnet ef database update

Question 12

What does LINQ stand for?

Answer 12

Language-Integrated Query

Question 13

a uniform query syntax in C# and VB.NET to retrieve data from different sources and formats. It is integrated in C# or VB, thereby eliminating the mismatch between programming languages and databases, as well as providing a single querying interface for different types of data sources.

Answer 13

LINQ

Question 14

3 parts of a query operation:

Answer 14

Data Source
Query
Execution

Question 15

Expressions that retrieve data from a data source

Answer 15

LINQ Queries

Question 16

a set of instructions that describes what data to retrieve from a given data source (or sources) and what type and organization the returned data should have.

Answer 16

query

Question 17

query expressed in query syntax

Answer 17

query expression

Question 18

what clause starts a query expression

Answer 18

from

Question 19

what clause ends a query expression

Answer 19

select or group

Question 20

how many clauses can be in a query expression

Answer 20

one or more

Question 21

what are some clauses?

Answer 21

where, orderby, join, let

Question 22

what does the INTO keyword in a query expression do?

Answer 22

enable the result of a join or group clause to serve as the source for additional query clauses in the same query expression

Question 23

From an application’s viewpoint, the specific type and structure of the original source data is not important

Answer 23

True

Question 24

The application always sees the source data as an IEnumerable or IQueryable collection.

Answer 24

True

Question 25

A query can: 1. Retrieve a subset of the elements to produce a new sequence without modifying the individual elements. The query may then sort or group the returned sequence in various ways 2. Retrieve a sequence of elements but transform them to a new type of object. 3. Retrieve a singleton value about the source data, such as: The number of elements that match a certain condition. The element that has the greatest or least value. The first element that matches a condition, or the sum of values in a specified set of elements.

Answer 25

True

Question 26

any variable that stores a query instead of the result of a query.

Answer 26

query variable

Question 27

A query variable is always an enumerable type that will produce a sequence of elements when it is iterated over in a foreach statement or a direct call to its IEnumerator.MoveNext method.

Answer 27

True

Question 28

By default, linq queries have deferred execution. This means that unless iterated via a foreach loop, the query isn’t going to retrieve data from the data source.

Answer 28

True

Question 29

You can force immediate execution by either using an aggregate function in the query such as count or by calling the ToList() or ToArray() methods.

Answer 29

True

Question 30

what are the ways to query using LINQ?

Answer 30

Query syntax and method syntax

Question 31

Used for retrieving data from the database

Answer 31

SELECT Statement

Question 32

The SELECT statement has several clauses:

Answer 32

``` Select From Where Group by Having Order by ```

Question 33

What is the logical order of operations to the SELECT statement

Answer 33

from, where, group by, having, select, order by

Question 34

Used to unnormalize 2 or more tables into one table, on a common column

Answer 34

JOIN

Question 35

What is an example syntax using JOIN?

Answer 35

SELECT * FROM Table_1 JOIN Table 2 ON Table_1.Id = Table_2.Table1Id

Question 36

what are the join types?

Answer 36

Inner (Default) Full Left Right

Question 37

Combines rows from both the queries

Answer 37

UNION

Question 38

Keeps only those rows which are common in both queries

Answer 38

INTERSECT

Question 39

Keeps rows from the left query which are not included in the right query

Answer 39

MINUS