Linq

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OverviewImplicitly typed local variables Anonymous TypesObject and Collection InitializationExtension MethodLambda ExpressionLinq

Virtual DiagramLINQAnonymosTypesImplicitly typed local variables Extension MethodObject and Collection InitializationLambda Expression

Implicitly typed local variablesSyntaxvar i = 5;var s = "Hello";var d = 1.0;var numbers = new int[] {1, 2, 3};var orders = new Easy to use

No need to define type RestrictionsThe declarator must include an initializer.The initializer must be an expression. The initializer cannot be an object or collection initializer by itself, but it can be a new expression that includes an object or collection initializer.The compile-time type of the initializer expression cannot be the null type.If the local variable declaration includes multiple declarators, the initializers must all have the same compile-time type.

var x; // Error, no initializer to infer type fromvar y = {1, 2, 3}; // Error, collection initializer not permittedvar z = null; // Error, null type not permitted

Anonymous TypesWhat is Anonymous types ?Create new types without defining itHow to define Anonymous types ?var pranay = new { id=1, Name= "pranay rana" };var krunal = new { id=1, Name= "krunal mevada" };Use of itvar user = from user in Users select new { user.Name, user.Id};

Object and Collection InitializationWhat is object Initialization ?create object without writing too much lengthy code and without invoking constructor.Exampleclass Employee{ public string Name { get; set; } public string Address { get; set; } public Employee(){} public Employee (string name) { Name= name; }}

Employee emp = new Employee() { Name="Pranay", Address="Ahmedabad" };orEmployee emp = new Employee("Hemang") { Address="Ahmedabad" };

Collection InitializationList<Employee> emp = new List<Employee> { new Employee { Name="Pranay", Address="Ahmedabad" }, new Employee { Name="Krunal",Address="Mevada" }, null };

Extension MethodWhat is Extesion Methods ?Allow programmer to "add" methods to existing types without creating a new derived type, recompiling, or by modifying the original typeExamplepublic static class Utilities{ public static string encryptString(this string str) { System.Security.Cryptography.MD5CryptoServiceProvider x = new System.Security.Cryptography.MD5CryptoServiceProvider(); byte[] data = System.Text.Encoding.ASCII.GetBytes(str); data = x.ComputeHash(data); return System.Text.Encoding.ASCII.GetString(data); }}

Lambda ExpressionReplacement of the anonymous method available in C#2.0Consist of single line or block of statement=> is lamda expression operatorSyntax( param ) => expr(int x) = > { return x + 1 };param => exprx=> x + 1;

Use of Lambda expressionC#2.0 by using anonymous method List<int> even = lstNumber.FindAll( delegate(inti) { if(i%2==) return i; }But for the C#3.0 with the lambda expression it will List<int> even = lstNumber.FindAll( i => (i%2) ==0 }In LINQvar order = orders.where( o=> o.ProcessStatus = ProcessStatus.Completed);

What is orm ?Object Relational Mapping Allow to map your database structure with the business layer model Hide low level database interaction detailsMake development easy and faster

LINQWhat is LINQ ?Language-Integrated Query Made up to make query any source of dataSome flavor of LINQLINQ to Object {Queries performed against the in-memory data}LINQ to SQL (formerly DLinq) {Queries performed against the relation database only Microsoft SQL Server Supported}LINQ to DataSet {Supports queries by using ADO.NET data sets and data tables}LINQ to Entities {Microsoft ORM solution}LINQ to XML (formerly XLinq) { Queries performed against the XML source}

SelectSQLSELECT * FROM [User]LINQ

var user = from u in Users select u;

Select with ColumnsSQL Select FirstName, LastName from [User]LINQfrom u in Users select new { u.FirstName, u.LastName };

Filter Selected DataSQLSelect firstname,LastName from [User] where id = 3LINQfrom u in Users where u.Id ==3select new { u.FirstName, u.LastName };

Filtering String DataSQLSELECT [Id], [FirstName], [LastName], [Email], [DisplayName], [Address1], [Address2], [Password], [Role] FROM [User] WHERE [Email] LIKE '%pranay%'LINQ from u in Users where u.Email.Contains ("pranay") select u;Or from u in Users where u.Email.StartsWith ("pranay") select u;

Inner JoinSQLSELECT [User].[Id], [FirstName], [LastName], [UserId], [MobileNo] FROM [User] INNER JOIN [UserClients] ON [User].[id] = [UserId]LINQvar user = from u in Users join uc in UserClients on u.Id equals uc.UserId select new { u.Id, u.FirstName, u.LastName, uc.MobileNo, uc.imeiNO, uc.Id, };

Outer JoinSQLSELECT [t0].[Id], [FirstName], [LastName], [UserId] AS [UserId], [MobileNo] AS [MobileNo] FROM [User] AS [t0] LEFT OUTER JOIN [UserClients] ON ([t0].[id]) = [UserId]LINQvar user = from u in Users join uc in UserClients on u.Id equals uc.UserId into myuserwithclient from m in myuserwithclient.DefaultIfEmpty() select new { u.Id, u.FirstName, u.LastName, m.UserId, m.MobileNo };

Ordering DataSQLSelect * from [User] order by firstNameLINQvar user = from u in Usersorderbyu.FirstNameselect new { u.FirstName, u.LastName };More than one columnvaremp = from e in dc.Employeesorderbye.Name, e.Desc select e;

Grouping DataSQLSELECT COUNT(*) AS [test], [UserId] FROM [UserClients] GROUP BY [UserId]LINQvar user = from u in UserClients group u by u.UserId into c select new { t1 = c.Key, tcount = c.Count() };

Filter Data Using IN and NOT IN ClausesSQLSELECT [Id], [UserId], [IMEINo] FROM [UserClients] WHERE [UserId] IN (3, 4)LINQint[] chosenOnes = { 3, 4 };var user = from u in UserClients where chosenOnes.Contains(u.UserId.Value) select new { u.id,u.userid, u.ImeiNo};

Filtering Data by Row NumbersSQLSELECT * FROM ( SELECT ROW_NUMBER() OVER (ORDER BY [id]) AS [ROW_NUMBER], [id], [FirstName], [LastName], [Email], [DisplayName], [Address1], [Address2], [Password], [Role] FROM [User] AS [t0] ) AS [t1] WHERE [t1].[ROW_NUMBER] BETWEEN 11 AND 20 ORDER BY [t1].[ROW_NUMBER]LINQvar users = from u in Users select u; varfilterUsers= users.OrderBy (p => p.Id).Skip (10).Take(10);

SQL ISNULL functionLINQvar user = from u in Users join uc in UserClients on u.Id equals uc.UserId into myuserwithclient from m in myuserwithclient.DefaultIfEmpty() select new { u.Id, FirstName= u.FirstName, LastName= u.LastName, UserId= m.UserId, MobileNo= m.MobileNo?? "N/A" };

SelectmanyFlattens the resulting sequences into one sequenceusers.SelectMany ( u => u.Userclient, (u, uc) => new { Name = u.Name, Mobileno = uc.Mobile, IsApproved = uc.IsApproved } )

Linq Deferred ExecutionQuery not going to execute at this point var query = from customer in db.Customers where customer.City == "Paris" select customer; Query get executed when we apply method like (Count(),toList() etc.)int count = (from customer in db.Customers where customer.City == "Paris" select customer).Count();

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