[HowTo] - Exploring the LINQ Universe (VB.Net)

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LINQ (Language-Integrated Query) is part of the .NET framework and offers capabilities for interacting with data, objects, or other sources within a particular syntax. This HowTo elaborates on the availability of LINQ and explores the offered functionalities

Current Version of this topic is DRAFT and will be finalized / enhanced soon

Introduction

Let’s recap the Example of LINQ from [HowTo] - First Start with LINQ (VB.Net).

Sample data:
myNumbers | List (Of Int32) = {12,34,5,8,10,2,15,7}.toList

Assignment:
Find all numbers in myNumbers where the number is greater than 10

Solutions

Essential:
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Method Syntax:
myNumbersFiltered | List (Of Int32) = myNumbers.Where(Function (x) x > 10).toList

Query Syntax:

myNumbersFiltered | List (Of Int32) = 
(From x in myNumbers
Where x > 10
Select x).toList

The availability of LINQ

In nontechnical words, the availability of LINQ depends on the datatype of a variable. A particular datatype exposes LINQ functionalities when a set of extension capabilities is present.

Also it is recommended to have the System.Linq namespace added to the imports
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a more technical summary

LINQ capabilities are available when a set of extension methods on the IEnumerable<T> interface is implemented and exposed.

LINQ Offerings

In general, LINQ is available on the datatype for the following sources:

  • LINQ To Objects: Array, List, Dictionary, String, DataTable
  • LINQ To Data: within the context of DataSet, SQL, Entity (Entity Framework)
  • LINQ to XML
  • Custom Sources: JSON offered by the Newtonsoft API

Following checks are intended to give some starting help and omit the more technical specifics and variants.

Check 1: direct availability

In case of uncertainty, the autocomplete feature (IntelliSense) can be used for checking if LINQ-related extension methods are presented.
The typical methods to check are: All, Any, Where, Select

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Check 2: availability over Cast()

In case of the above-mentioned methods are not offered following check can be done:

  • is there a GetEnumerator method?
  • is there a Cast method?
    In a lot of cases, LINQ methods can be made available by using the Cast method on first
Examples

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Check 3: AsEnumerable method, Datatables

LINQ can be used on a variable after transforming it into a collection of datatype EnumerableXXX<T>

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Same example in Query Syntax

(From d in dtData.AsEnumerable()
Where d(2).ToString.Equals("Y")
Select r = d).CopyToDataTable

Overview LINQ capabilities - Operators

The following table gives a short overview of the LINQ standard operators (LINQ methods)

Group Operators
Restriction (Filtering) Where
Projection (Selection) Select, SelectMany
Ordering OrderBy, OrderByDescending, Reverse, ThenBy, ThenByDescending
Quantifiers All, Any, Contains
Join Join (inner join), GroupJoin (left outer join)
Grouping GroupBy
Aggregation Aggregate, Count, LongCount, Max, Min, Sum, Average
Partitioning (Paging) Skip, SkipWhile, Take, TakeWhile
Set Distinct, Except, Intersect, Union
Conversion AsEnumerable, Cast, OfType, ToArray, ToDictionary, ToList, ToLookup
Element Access ElementAt, ElementAtOrDefault, First, FirstOrDefault, Last, LastOrDefault, Single, SingleOrDefault
Conjunction Concat, Append, Prepend
Generation DefaultIfEmpty, Empty, Range, Repeat
Other SequenceEqual, Zip

References

Questions

For questions on your retrieval case open a new topic and get individual support

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