LINQ

(Language Integrated Query)

TIMELINE

TIMELINE

Contents

  • Introduction to LINQ

  • Purpose of LINQ

  • Advantages of LINQ

  • Disadvantages of LINQ

  • LINQ Syntax

- Query Syntax

   - Method Syntax

LINQ ?

A set of technologies based on the integration of query capabilities directly into the C# language

WHY LINQ ?

 LINQ is simpler, tidier, and higher-level than SQL.

 When it comes to querying databases, In most cases, LINQ is more productive querying language than SQL.

LINQ Architecture

ADVANTAGES of LINQ 

  • Full type checking at compile time

  • Has IntelliSense (can avoid silly errors)

  • Query can be reused

  • Can debug using .NET debugger

  • Suport filtering, sorting, ordering, grouping with much less effort.

DISADVANTAGES of LINQ 

  • Writing complex queries is LINQ is a bit tedious as compared to SQL

  • The performance is degraded - if the query is not written properly

  • Need to build the project and deploy the DDL every time  has a changes.

LINQ Execution

Syntax of LINQ

  1. Query Syntax

  2. Method Syntax

var numbers = Enumerable.Range(1, 100); //1,2,...,100
//query syntax:
var query = from n in numbers
    where n % 3 == 0
    select n * 2;
var numbers = Enumerable.Range(1, 100);
//method syntax
var method = numbers
    .Where(n => n % 3 == 0)
    .Select(n => n * 2);

LINQ Query Syntax

from object in datasource

where condition

select object

Initialization

Condition

Selection

 // Select all EBs.
 var ebs = (from e in _dataContext.EBs
            select e).ToList();

LINQ Query Syntax

from object in datasource

where condition

select object

Initialization

Condition

Selection

// Select all approved form submissions.
var formSubmissions = (from s in _dataContext.FormSubmissions
                       where s.status == FormSubmission.STATUS_APPROVED
                       select s).ToList();

LINQ Query Syntax

LINQ Query Syntax

 // Load FormEB record.
var formEB = await (from r in _dataContext.FormEBs
                    where r.listing_job_id == listingJobId
                    && r.fe_email == email
                    && r.eb_id == ebId
                    select r).AsNoTracking().FirstAsync();
OPERATOR DESCRIPTION
where Returns values from the datasource based on a predicate function.
AsNoTeacking() returns a new query and the returned entities will not be cached by the context (DbContext or Object Context)
FirstAsync() Asynchronously returns the first element of the query that satisfies a specified condition.

LINQ Method Syntax

DataSource

.ConditionMethod()

.SelectionMethod()

Initialization

Condition

Selection

// Get all photos for this EE.
var localEePhotos = localJobPhotos
                    .Where(x => x.uid == localEE.uid)
                    .ToList();

LINQ Method Syntax

LINQ Method Syntax

// Get all photos for this EE.
var localEePhotos = localJobPhotos
                    .Where(x => x.uid == localEE.uid)
                    .ToList();
OPERATOR DESCRIPTION
.ToList() Takes the elements from the given source and it returns a new List.
The input would be converted to type List.

References

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