What is Language Integrated Query (LINQ)?
LINQ is a set of extensions to .NET Framework that encapsulate language integrated query, set and other
transformation operations. It extends VB, C# with their language syntax for queries. It also provides class
libraries which allow a developer to take advantages of these features.
Difference between LINQ and Stored Procedures:
Stored procedures normally are faster as they have a predictable execution plan. Therefore, if a stored procedure is being executed for the second time, the database gets the cached execution plan to execute the stored procedure.
LINQ supports type safety against stored procedures.
LINQ supports abstraction which allows framework to add additional improvements like multi threading. It’s much simpler and easier to add this support through LINQ instead of stored procedures.
LINQ allows for debugging using .NET debugger, which is not possible in case of stored procedures.
LINQ supports multiple databases against stored procedures which need to be re-written for different databases.
Deploying LINQ based solution is much simpler than a set of stored procedures
Pros and cons of LINQ (Language-Integrated Query)
Pros of LINQ:
Supports type safety
Supports abstraction and hence allows developers to extend features such as multi threading.
Easier to deploy
Simpler and easier to learn
Allows for debugging through .NET debugger.
Support for multiple databases
Cons of LINQ:
LINQ needs to process the complete query, which might have a performance impact in case of complex queries
LINQ is generic, whereas stored procedures etc can take full advantage of database features.
If there has been a change, the assembly needs to be recompiled and redeployed.
Disadvantages of LINQ over stored procedures:
LINQ needs to process the complete query, which might have a performance impact in case of complex queries against stored procedures which only need serialize sproc-name and argument data over the network.
LINQ is generic, whereas stored procedures etc can take full advantage of the complete database features.
If there has been a change, the assembly needs to be recompiled and redeployed whereas stored procedures are much simpler to update.
It’s much easier to restrict access to tables in database using stored procedures and ACL’s than through LINQ.
Can I use LINQ with databases other than SQL Server? Explain how
LINQ supports Objects, XML, SQL, Datasets and entities. One can use LINQ with other
databases through LINQ to Objects or LINQ to Datasets, where the objects and datasets then
take care of database specific operations and LINQ only needs to deal with those objects, not the
database operations directly.
What is Linq to SQL Deferred Loading?
(C#) -Deferred Loading is a property of Linq to sql, by default it is set true,
Exam – Let’s have two tables -
Blogs Table (BlogID ,Blog Name,owner) and Post table ( PostID, BlogID, Title, Body)
To find Name and No’s of posts in each blog-
BlogDataContext ctx = new BlogDataContext( );
var query = from b in ctx.Blogs select b;
foreach (Blog b in query)
{
Console.WriteLine("{0} has {1} posts", b.BlogName, b.Posts.Count);
}
Output of queries Produce Blog name with no’s of post, But For each
Blog
Looping will be occurs (in case long list of blogs) that’s reduces Overall
Performance that’s called the Deferred loading.
Write a Program using Skip and Take operators. How can it beneficial for bulky data accessing on page?
“skip” and “take” Operator used for Paging. Suppose we have Customer table of 100 records. To
find 10 records by skipping the first 50 records from customer table-
Public void Pagingdatasource ()
{
Var Query =from CusDetails in db.customer skip (50) Take (10)
ObjectDumper.Write(q)
}
Hence The LinQ “ SKIP” operator lets you skip the results you want, and “Take” Operator
enables you yo select the rest of result . So By Using Skip and Take Operator, You can create
paging of Specific sequence.
Write a Program for Concat to create one sequence of Data Rows that contains DataTables's
Data Rows, one after the other.
(C#)
Public void Datasetlinq()
{
var numbersA = TestDS.Tables("NumbersA").AsEnumerable();
var numbersB = TestDS.Tables("NumbersB").AsEnumerable();
var allNumbers = numbersA.Concat(numbersB);
Console.WriteLine("All numbers from both arrays:");
foreach (object n_loopVariable in allNumbers) {
n = n_loopVariable;
Console.WriteLine(n["number"]);
}
}
How can you find average of student marks from student tables (Columns are StudentID, Marks)?
(C#)
Public void LinqToSqlAverage()
{
var query = (from p in db. student. Marks).Average();
Console.WriteLine(q);
}
What is Lambda Expressions? How can we optimize our linq code using this Expression?
Lambda expressions can be considered as a functional superset of anonymous
methods, providing the following additional functionality:
Lambda expressions can infer parameter types, allowing you to omit them.
Lambda expressions can use both statement blocks and expressions as bodies,
allowing for a terser syntax than anonymous methods, whose bodies can
only be statement blocks.
Lambda expressions can participate in type argument inference and
method overload resolution when passed in as arguments. Note: anonymous
methods can also participate in type argument inference (inferred return types).
In C#, a lambda expression is written as a parameter list, followed by the => token,followed by an
expression or a statement block
What is “OfType” in linq?
public void TypeofExa()
{
Var numbers = {null,1.0,"two", 3,"four",5,"six",7.0 };
var doubles = from n in numbers where n is doublen;
Console.WriteLine("Numbers stored as doubles:");
foreach (object d in doubles)
{
Console.WriteLine(d);
}
}
Output:
Numbers stored as doubles:
1
7
How can we find Sequence of Items in two different array (same Type) in the same order using linq query?
Public void MatchSequenceLinq()
{
Var wordsA = {"Rahul","ashok","sweta"};
Var wordsB = {"rahul","ashok","sweta"};
var match = wordsA.SequenceEqual(wordsB);
Console.WriteLine("The sequences match: {0}", match);
}
Output Result: True
Differentiate between Conversion Operator “IEnumerable” and “ToDictionary” of linq.
IEnumerable and To Dictionary both are Conversion Operator which are used to solved to
conversion type Problems.
“AsEnumerable ” operator simply returns the source sequence as an object of type
IEnumerable<T>. This kind of “conversion on the fly” makes it possible to call the general-
purpose extension methods over source, even if its type has specific implementations of them
Signature-
public static IEnumerable<T> AsEnumerable<T>
(
this IEnumerable<T> source
);
“ToDictionary ” Conversion Operator is the instance of Dictionary (k,T) .
The “keySelector ”predicate identifies the key of each item while
“elementSelector ”, if provided, is used to extract each single item.
Key and elementSelector Predicate can be Used in following ways-
Example-
Public void ToDictionatyExample()
{
Var scoreRecords=
{
new {Name = "Alice",Score = 50 },
new {Name = "Bob",Score = 40 },
new {Name = "Cathy", Score = 45} };
Var scoreRecordsDict = scoreRecords.ToDictionary(sr => sr.Name);
Console.WriteLine("Bob's score: {0}", scoreRecordsDict("Bob"));
}
Result: Bob's score: { Name = Bob, Score = 40 }
List out the Data Context Functions. Where do we use “SubmitChanges()”?
Create Database ()/Delete database ()
Database Exist ( )
Submit Changes ()
Create Query()
Log
SubmitChanges()- SunbmitChanges Data Context Fuction Used to submit any update to the actual
database.
Why do we use “Contains” method for strings type functions?
Contains method Used to find all matching records From Given string using
Matching keywords,
Example-
This Examples returns the Customer Names from Customer tables whose Names have contains
“Anders”
Public void LinqToSqlStringUsingContains()
{
Var q = From c In db.Customers _
Where c.ContactName.Contains("Anders") _
Select c
ObjectDumper.Write(q)
}
Partition following list of numbers by their remainder when divided by “3”-{Var numbers() = {5, 4,
1, 3, 9, 8, 6, 7, 2, 0}}
(Vb)
Public Sub PartitioningExample()
Dim numbers() = {5, 4, 1, 3, 9, 8, 6, 7, 2, 0}
Dim numberGroups = From n In numbers Group n By key = n Mod 3
Into Group _
Select Remainder = key, NumberGroup = Group
For Each g In numberGroups
Console.WriteLine("Numbers with a remainder of {0} when divided by
3:", g.Remainder)
For Each n In g.NumberGroup
Console.WriteLine(n)
Next
Next
End Sub
Can you Concat two arrays to create one sequence that contains each array's values, one after the other?
Var ArrayA[]={4,8,7,9,4,7}
Var ArraB[] ={8,2,5,7,8,1}
Answers(vb)
Public Sub ConcatenateTwoArray()
Dim numbersA() = {4, 8, 7, 9, 4, 7}
Dim numbersB() = {8, 2, 5, 7, 8,1}
Dim allNumbers = numbersA.Concat(numbersB)
Console.WriteLine("All numbers from both arrays:")
For Each n In allNumbers
Console.WriteLine(n)
Next
End Sub
Output:{4,8,7,9,4,7,8,2,5,7,8,1}
Write small Program to generate Xml Document from table like (StudentRecord Table) using linq query
Public void CreateXmlDocFromArray()
{
// Now enumerate over the array to build an XElement.
XElement StudentRecords =
new XElement("StudentInfo",
from c in Student
select new XElement("Student",
new XAttribute("Name", c.Name),
new XElement("RollNo", c.RollNo)
)
);
Console.WriteLine(StudentRecords);
}
What is Quantifiers in reference linq to Dataset?
Quantifier Operators return the Boolean value (either True or false) if some or all the elements in
a sequence satisfy a condition,
Mainly two Quantifiers in linq –
Any-
All
Examples (vb)
“Any” to determine if any of the words in the array contain the substring
Public Sub ExampleAny()
Dim words() = {"believe", "relief", "receipt", "field"}
Dim iAfterE = words.Any(Function(w) w.Contains("ei"))
Console.WriteLine("There is a word that contains in the list that contains 'ei': {0}", iAfterE)
End Sub
Result:
There is a word that contains in the list that contains 'ei': True
“All “to return a grouped a list of products only for categories that have all of their products in stock
Public Sub Quantifier_All_Exam()
Dim products = GetProductList()
Dim productGroups = From p In products _
Group p By p.Category Into Group _
Where (Group.All(Function(p) p.UnitsInStock > 0)) _
Select Category, ProductGroup = Group
ObjectDumper.Write(productGroups, 1)
End Sub
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