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CS313D: ADVANCED
PROGRAMMING LANGUAGE
Lecture 10: introduction to LINQ Computer Science
department
Lecture Contents
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What is LINQ?
What is a query?
Query on arrays
Query on a Generic List
Query
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A query: to request information that
satisfies given criteria.
SQL is the international standard used to
perform and to manipulate data in a database.
LINQ (Language-Integrated Query) allow to
write query expressions that retrieve
information from a variety of data sources, not
just databases.
LINQ to Objects can be used to filter arrays and
Lists, selecting elements that satisfy a set of
conditions
Using LINQ on Arrays
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Repetition statements that filter arrays focus on the
steps required to get the results imperative
programming.
LINQ queries, specify what to do not how to do it
declarative programming
Example
from
specifies a
range
variable and
the data
source to
query
the where
specifies the
condition
select
determines
the results
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Example
The orderby
clause sorts
the query
results in
ascending
order.
The
descending
modifier sorts
the results in
descending
order.
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Example
A LINQ query
returns an
IEnumerable<T>
object
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Using LINQ on an Array of Objects
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LINQ is not limited to querying arrays of simple
types such as integers.
The following example uses LINQ to query an
array of Employee objects.
The Employee Class
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Test App
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Test App
conditional
AND (&&)
operator can
be used to
combine
conditions.
An orderby
clause can
sort the results
according to
multiple
properties
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Test App
Any checks if there is at least one element.
First returns the first element in the result.
Distinct removes duplicate elements
Projection performs a transformation on the data
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Test App
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When the
compiler
creates an
anonymous
type, it
automatically
generates a
ToString
method that
returns a
string
representation
of the object.
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Querying a Generic Collection
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You can use LINQ to Objects to query List just as arrays.
Although commonly used, arrays have limited capabilities.
A List is similar to an array but provides additional functionality, such as dynamic resizing.
Example
let used to
create a new
range
variable to
store a
temporary
result for use
later in the
LINQ query.
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Chapter 9: 9.1, 9.2, 9.3, 9.5
That’s all
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Case Study 21
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Q:
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