C# What is the difference between IEnumerable and IQueryable?

What is the difference between IEnumerable and IQueryable?

IEnumerable and IQueryable may seem like the same at a quick glance, but there are important differences that us, as developers must be aware so that we not only get a working product out the door but also something that performs well.

IEnumerable	IQueryable
·         IEnumerable exists in the System. Collections namespace.	·         IQueryable exists in the System.Linq Namespace.
·         IEnumerable is suitable for querying data from in-memory collections like List, Array and so on. ·          Example:  IEnumerable<Emp> emp = ent.Emps; IEnumerable<Emp> temp = emp.Where(x => x.Empid ==5).ToList<Emp>(); This where filter is executed on the client side where the “IEnumerable” code is. In other words, all the data is fetched from the database and then at the client it scans and gets the record with “EmpId” is “5”.	·         IQueryable is suitable for querying data from out-memory like remote database collections. ·         Example : In this case, the filter is applied on the database using the “SQL” query. So the client sends a request and on the server side, a select query is fired on the database and only necessary data is returned.
·         IEnumerable not supported Lazy Loading . Hence not suitable for paging like scenarios.	·         IQueryable supported Lazy Loading .
·         While querying data from the database, IEnumerable executes "select query" on the server-side, loads data in-memory on the client-side and then filters the data.	·         While querying data from a database, IQueryable executes a "select query" on server-side with all filters.
·         IEnumerable is beneficial for LINQ to Object and LINQ to XML queries.	·         IQueryable is beneficial for LINQ to SQL queries. ·         IQueryable

Using Generics With C#

Using Generics With C#

Generics are most frequently used with collections and the methods that operate on them. Version 2.0 of the .NET Framework class library provides a new namespace, System.Collections.Generic, which contains several new generic-based collection classes.

Generics are different from generic collections. Generic collections are emerged from generic concept. It helps us to maximize code reuse, performance and type safety.

Generics are strongly type collections.

Generics help to decouple the data-type from the logical code snippet which makes the code to reuse again and again.

We can also create classes and pass to it the generic parameter as type.

We can use generics in our code by calling the namespace "using System.Collections.Generic;".

Microsoft applied generic concept on

.NET collections to make generic collections.

Arraylist to make list generic collections.

Hashtables to make Dictionary.

Stacks and Queues to make Stacks and Queues generics.

Example:   public class GenericsClass<T>

    {

   public bool Compare( T a , T b)

        {

            if(a.Equals( b))

            {

                return true;

            }

            return false;

        }    }

     }

    class Program

    {

    public static void Main()

    {

            GenericsClass<int> obj = new GenericsClass<int>();

            bool checkintData =  obj.Compare(10, 10);

            Console.WriteLine("Int data Check:{0}", checkintData);

            GenericsClass<string> obj1 = new GenericsClass<string>();

            bool StringData = obj1.Compare("indian", "indian");

            Console.WriteLine("String data Check:{0}", StringData);    }

    }

OutPut :  True, True

Advantages of Generic:

Type safety - this ensures that the method, class, or interface etc. works only on the correct data type. For example, if you use string when calling a generic method, then all the values passed in as expected to be strings. If you pass in an int value parameter, the compiler will detect that as an error and the program will not be able to compile.

Errors/Exceptions are caught at compile time as opposed to runtime errors/exceptions - if given a choice between compile time and runtime errors, 100% of developers choose compile time errors so should you. The last thing we want is errors crashing the program when the users are working with it.

Re-usability & Flexibility - in the above example on the problem statement, we declared more than one method and the only difference was the data type of the parameters that we passed. With generics, you only have to create one method and re-use it with any data type that you want

Write clean code - we do not need to write methods, class or interfaces that contain complex logic that checks the data type of the parameter values passed in.

Quickly Rename a Mysql database

How do I quickly rename a MySQL database (change schema name)?

From phpMyAdmin, select the database you want to select. In the tabs there's one called Operations, go to the rename section. That's all.

It does, as many suggested, create a new database with the new name, dump all tables of the old database into the new database and drop the old database.