What is the difference between IQueryable T and IEnumerable T

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What is the difference between IQueryable lt T gt  and IEnumerable lt T gt      See also What s the difference between IQueryable and IEnumerable that overlaps with this question

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In real life  if you are using a ORM like LINQ-to-SQL   If you create an IQueryable  then the query may be converted to sql and run on the database server If you create an IEnumerable  then all rows will be pulled into memory as objects before running the query    In both cases if you don t call a ToList   or ToArray   then query will be executed each time it is used  so  say  you have an IQueryable lt T gt  and you fill 4 list boxes from it  then the query will be run against the database 4 times   Also if you extent your query   q Where x name    a   ToList     Then with a IQueryable the generated SQL will contains    where name      a     but with a IEnumerable many more roles will be pulled back from the database  then the x name      a    check will be done by  NET

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IEnumerable   IEnumerable is best suitable for working with in-memory collection  or local queries   IEnumerable doesn   t move between items  it is forward only collection   IQueryable  IQueryable best suits for remote data source  like a database or web service   or remote queries   IQueryable is a very powerful feature that enables a variety of interesting deferred execution scenarios  like paging and composition based queries    So when you have to simply iterate through the in-memory collection  use IEnumerable  if you need to do any manipulation with the collection like Dataset and other data sources  use IQueryable

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In simple words other major difference is that  IEnumerable execute select query on server side  load data in-memory on client side and then filter data while IQueryable execute select query on server side with all filters

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IQueryable is faster than IEnumerable if we are dealing with huge amounts of data from database because IQueryable gets only required data from database where as IEnumerable gets all the data regardless of the necessity from the database

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We use IEnumerable and IQueryable to manipulate the data that is retrieved from database  IQueryable inherits from IEnumerable  so IQueryable does contain all the IEnumerable features  The major difference between IQueryable and IEnumerable is that IQueryable executes query with filters whereas IEnumerable executes the query first and then it filters the data based on conditions   Find more detailed differentiation below    IEnumerable    IEnumerable exists in the System Collections namespace IEnumerable execute a select query on the server side  load data in-memory on a client-side and then filter data IEnumerable is suitable for querying data from in-memory collections like List  Array IEnumerable is beneficial for LINQ to Object and LINQ to XML queries   IQueryable    IQueryable exists in the System Linq namespace IQueryable executes a  select query  on server-side with all filters IQueryable is suitable for querying data from out-memory  like remote database  service  collections IQueryable is beneficial for LINQ to SQL queries   So IEnumerable is generally used for dealing with in-memory collection  whereas  IQueryable is generally used to manipulate collections

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IEnumerable   IEnumerable is best suitable for working with in-memory collection  or local queries   IEnumerable doesn   t move between items  it is forward only collection   IQueryable  IQueryable best suits for remote data source  like a database or web service   or remote queries   IQueryable is a very powerful feature that enables a variety of interesting deferred execution scenarios  like paging and composition based queries    So when you have to simply iterate through the in-memory collection  use IEnumerable  if you need to do any manipulation with the collection like Dataset and other data sources  use IQueryable

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Here is what I wrote on a similar post  on this topic    And no  I don t usually quote myself  but these are very good articles     This article is helpful  IQueryable vs IEnumerable in LINQ-to-SQL   Quoting that article   As per the MSDN documentation  calls made on IQueryable operate by building up the internal expression tree instead   These methods that extend IQueryable Of T  do not perform any querying directly  Instead  their functionality is to build an Expression object  which is an expression tree that represents the cumulative query      Expression trees are a very important construct in C  and on the  NET platform   They are important in general  but C  makes them very useful   To better understand the difference  I recommend reading about the differences between expressions and statements in the official C  5 0 specification here  For advanced theoretical concepts that branch into lambda calculus  expressions enable support for methods as first-class objects  The difference between IQueryable and IEnumerable is centered around this point  IQueryable builds expression trees whereas IEnumerable does not  at least not in general terms for those of us who don t work in the secret labs of Microsoft   Here is another very useful article that details the differences from a push vs  pull perspective   By  push  vs   pull   I am referring to direction of data flow  Reactive Programming Techniques for  NET and C   Here is a very good article that details the differences between statement lambdas and expression lambdas and discusses the concepts of expression tress in greater depth  Revisiting C  delegates  expression trees  and lambda statements vs  lambda expressions

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Below mentioned small test might help you understand one aspect of difference between IQueryable lt T gt  and IEnumerable lt T gt   I ve reproduced this answer from this post where I was trying to add corrections to someone else s post  I created following structure in DB  DDL script    CREATE TABLE  dbo   Employee   PersonId   int  NOT NULL PRIMARY KEY  Salary   int  NOT NULL    Here is the record insertion script  DML script    INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 1  20  INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 2  30  INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 3  40  INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 4  50  INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 5  60  GO   Now  my goal was to simply get top 2 records from Employee table in database   I added an ADO NET Entity Data Model item into my console application pointing to Employee table in my database and started writing LINQ queries   Code for IQueryable route   using  var efContext   new EfTestEntities          IQueryable lt int gt  employees   from e in efContext Employees  select e Salary      employees   employees Take 2        foreach  var item in employees                Console WriteLine item             When I started to run this program  I had also started a session of SQL Query profiler on my SQL Server instance and here is the summary of execution    Total number of queries fired  1 Query text  SELECT TOP  2   c   Salary  AS  Salary  FROM  dbo   Employee  AS  c    It is just that IQueryable is smart enough to apply the Top  2  clause on database server side itself so it brings only 2 out of 5 records over the wire  Any further in-memory filtering is not required at all on client computer side   Code for IEnumerable route   using  var efContext   new EfTestEntities          IEnumerable lt int gt  employees   from e in efContext Employees  select e Salary      employees   employees Take 2        foreach  var item in employees                Console WriteLine item             Summary of execution in this case    Total number of queries fired  1 Query text captured in SQL profiler  SELECT  Extent1   Salary  AS  Salary  FROM  dbo   Employee  AS  Extent1    Now the thing is IEnumerable brought all the 5 records present in Salary table and then performed an in-memory filtering on the client computer to get top 2 records  So more data  3 additional records in this case  got transferred over the wire unnecessarily

User · Answer

ienumerable when we want to deal with inprocess memory  i e without dataconnection iqueryable when to deal with sql server  i e with data connection ilist   operations like add object  delete object etc

User · Answer

The primary difference is that the LINQ operators for IQueryable lt T gt  take Expression objects instead of delegates  meaning the custom query logic it receives  e g   a predicate or value selector  is in the form of an expression tree instead of a delegate to a method   IEnumerable lt T gt  is great for working with sequences that are iterated in-memory  but IQueryable lt T gt  allows for out-of memory things like a remote data source  such as a database or web service   Query execution   Where the execution of a query is going to be performed  quot in process quot   typically all that s required is the code  as code  to execute each part of the query   Where the execution will be performed out-of-process  the logic of the query has to be represented in data such that the LINQ provider can convert it into the appropriate form for the out-of-memory execution - whether that s an LDAP query  SQL or whatever    More in   LINQ   IEnumerable lt T gt  and IQueryable lt T gt  C  3 0 and LINQ   quot Returning IEnumerable lt T gt  vs IQueryable lt T gt  quot  Reactive Programming for  NET and C  Developers - An Introduction To IEnumerable  IQueryable  IObservable  and IQbservable 2018   quot THE MOST FUNNY INTERFACE OF THE YEAR     IQUERYABLE lt T gt  quot  from Bart De Smet

User · Answer

The primary difference is that the LINQ operators for IQueryable lt T gt  take Expression objects instead of delegates  meaning the custom query logic it receives  e g   a predicate or value selector  is in the form of an expression tree instead of a delegate to a method   IEnumerable lt T gt  is great for working with sequences that are iterated in-memory  but IQueryable lt T gt  allows for out-of memory things like a remote data source  such as a database or web service   Query execution   Where the execution of a query is going to be performed  quot in process quot   typically all that s required is the code  as code  to execute each part of the query   Where the execution will be performed out-of-process  the logic of the query has to be represented in data such that the LINQ provider can convert it into the appropriate form for the out-of-memory execution - whether that s an LDAP query  SQL or whatever    More in   LINQ   IEnumerable lt T gt  and IQueryable lt T gt  C  3 0 and LINQ   quot Returning IEnumerable lt T gt  vs IQueryable lt T gt  quot  Reactive Programming for  NET and C  Developers - An Introduction To IEnumerable  IQueryable  IObservable  and IQbservable 2018   quot THE MOST FUNNY INTERFACE OF THE YEAR     IQUERYABLE lt T gt  quot  from Bart De Smet

User · Answer

First of all  IQueryable lt T gt  extends the IEnumerable lt T gt  interface  so anything you can do with a  plain  IEnumerable lt T gt   you can also do with an IQueryable lt T gt     IEnumerable lt T gt  just has a GetEnumerator   method that returns an Enumerator lt T gt  for which you can call its MoveNext   method to iterate through a sequence of T   What IQueryable lt T gt  has that IEnumerable lt T gt  doesn t are two properties in particular   one that points to a query provider  e g   a LINQ to SQL provider  and another one pointing to a query expression representing the IQueryable lt T gt  object as a runtime-traversable abstract syntax tree that can be understood by the given query provider  for the most part  you can t give a LINQ to SQL expression to a LINQ to Entities provider without an exception being thrown    The expression can simply be a constant expression of the object itself or a more complex tree of a composed set of query operators and operands  The query provider s IQueryProvider Execute   or IQueryProvider CreateQuery   methods are called with an Expression passed to it  and then either a query result or another IQueryable is returned  respectively

User · Answer

We use IEnumerable and IQueryable to manipulate the data that is retrieved from database  IQueryable inherits from IEnumerable  so IQueryable does contain all the IEnumerable features  The major difference between IQueryable and IEnumerable is that IQueryable executes query with filters whereas IEnumerable executes the query first and then it filters the data based on conditions   Find more detailed differentiation below    IEnumerable    IEnumerable exists in the System Collections namespace IEnumerable execute a select query on the server side  load data in-memory on a client-side and then filter data IEnumerable is suitable for querying data from in-memory collections like List  Array IEnumerable is beneficial for LINQ to Object and LINQ to XML queries   IQueryable    IQueryable exists in the System Linq namespace IQueryable executes a  select query  on server-side with all filters IQueryable is suitable for querying data from out-memory  like remote database  service  collections IQueryable is beneficial for LINQ to SQL queries   So IEnumerable is generally used for dealing with in-memory collection  whereas  IQueryable is generally used to manipulate collections

User · Answer

This is a nice video on youtube which demonstrates how these interfaces differ   worth a watch    Below goes a long descriptive answer for it   The first important point to remember is IQueryable interface inherits from IEnumerable  so whatever IEnumerable can do  IQueryable can also do     There are many differences but let us discuss about the one big difference which makes  the biggest difference  IEnumerable interface is useful when your collection is loaded using LINQ or Entity framework and you want to apply filter on the collection   Consider the below simple code which uses IEnumerable with entity framework  It   s using a Where filter to get records whose EmpId is 2   EmpEntities ent   new EmpEntities    IEnumerable lt Employee gt  emp   ent Employees   IEnumerable lt Employee gt  temp   emp Where x   gt  x Empid    2  ToList lt Employee gt       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 its scans and gets the record with EmpId is 2     But now see the below code we have changed IEnumerable to IQueryable  It creates a SQL Query at the server side and only necessary data is sent to the client side   EmpEntities ent   new EmpEntities    IQueryable lt Employee gt  emp   ent Employees  IQueryable lt Employee gt  temp    emp Where x   gt  x Empid    2  ToList lt Employee gt         So the difference between IQueryable and IEnumerable is about where the filter logic is executed  One executes on the client side and the other executes  on the database   So if you working with only in-memory data collection IEnumerable is a good choice but if you want to query data collection which is connected with database  IQueryable is a better choice as it reduces network traffic and uses the power of SQL language

User · Answer

This is a nice video on youtube which demonstrates how these interfaces differ   worth a watch    Below goes a long descriptive answer for it   The first important point to remember is IQueryable interface inherits from IEnumerable  so whatever IEnumerable can do  IQueryable can also do     There are many differences but let us discuss about the one big difference which makes  the biggest difference  IEnumerable interface is useful when your collection is loaded using LINQ or Entity framework and you want to apply filter on the collection   Consider the below simple code which uses IEnumerable with entity framework  It   s using a Where filter to get records whose EmpId is 2   EmpEntities ent   new EmpEntities    IEnumerable lt Employee gt  emp   ent Employees   IEnumerable lt Employee gt  temp   emp Where x   gt  x Empid    2  ToList lt Employee gt       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 its scans and gets the record with EmpId is 2     But now see the below code we have changed IEnumerable to IQueryable  It creates a SQL Query at the server side and only necessary data is sent to the client side   EmpEntities ent   new EmpEntities    IQueryable lt Employee gt  emp   ent Employees  IQueryable lt Employee gt  temp    emp Where x   gt  x Empid    2  ToList lt Employee gt         So the difference between IQueryable and IEnumerable is about where the filter logic is executed  One executes on the client side and the other executes  on the database   So if you working with only in-memory data collection IEnumerable is a good choice but if you want to query data collection which is connected with database  IQueryable is a better choice as it reduces network traffic and uses the power of SQL language

User · Answer

The primary difference is that the LINQ operators for IQueryable lt T gt  take Expression objects instead of delegates  meaning the custom query logic it receives  e g   a predicate or value selector  is in the form of an expression tree instead of a delegate to a method   IEnumerable lt T gt  is great for working with sequences that are iterated in-memory  but IQueryable lt T gt  allows for out-of memory things like a remote data source  such as a database or web service   Query execution   Where the execution of a query is going to be performed  quot in process quot   typically all that s required is the code  as code  to execute each part of the query   Where the execution will be performed out-of-process  the logic of the query has to be represented in data such that the LINQ provider can convert it into the appropriate form for the out-of-memory execution - whether that s an LDAP query  SQL or whatever    More in   LINQ   IEnumerable lt T gt  and IQueryable lt T gt  C  3 0 and LINQ   quot Returning IEnumerable lt T gt  vs IQueryable lt T gt  quot  Reactive Programming for  NET and C  Developers - An Introduction To IEnumerable  IQueryable  IObservable  and IQbservable 2018   quot THE MOST FUNNY INTERFACE OF THE YEAR     IQUERYABLE lt T gt  quot  from Bart De Smet

User · Answer

Below mentioned small test might help you understand one aspect of difference between IQueryable lt T gt  and IEnumerable lt T gt   I ve reproduced this answer from this post where I was trying to add corrections to someone else s post  I created following structure in DB  DDL script    CREATE TABLE  dbo   Employee   PersonId   int  NOT NULL PRIMARY KEY  Salary   int  NOT NULL    Here is the record insertion script  DML script    INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 1  20  INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 2  30  INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 3  40  INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 4  50  INSERT INTO  EfTest   dbo   Employee    PersonId   Salary  VALUES 5  60  GO   Now  my goal was to simply get top 2 records from Employee table in database   I added an ADO NET Entity Data Model item into my console application pointing to Employee table in my database and started writing LINQ queries   Code for IQueryable route   using  var efContext   new EfTestEntities          IQueryable lt int gt  employees   from e in efContext Employees  select e Salary      employees   employees Take 2        foreach  var item in employees                Console WriteLine item             When I started to run this program  I had also started a session of SQL Query profiler on my SQL Server instance and here is the summary of execution    Total number of queries fired  1 Query text  SELECT TOP  2   c   Salary  AS  Salary  FROM  dbo   Employee  AS  c    It is just that IQueryable is smart enough to apply the Top  2  clause on database server side itself so it brings only 2 out of 5 records over the wire  Any further in-memory filtering is not required at all on client computer side   Code for IEnumerable route   using  var efContext   new EfTestEntities          IEnumerable lt int gt  employees   from e in efContext Employees  select e Salary      employees   employees Take 2        foreach  var item in employees                Console WriteLine item             Summary of execution in this case    Total number of queries fired  1 Query text captured in SQL profiler  SELECT  Extent1   Salary  AS  Salary  FROM  dbo   Employee  AS  Extent1    Now the thing is IEnumerable brought all the 5 records present in Salary table and then performed an in-memory filtering on the client computer to get top 2 records  So more data  3 additional records in this case  got transferred over the wire unnecessarily

User · Answer

In simple words other major difference is that  IEnumerable execute select query on server side  load data in-memory on client side and then filter data while IQueryable execute select query on server side with all filters

User · Answer

The primary difference is that the LINQ operators for IQueryable lt T gt  take Expression objects instead of delegates  meaning the custom query logic it receives  e g   a predicate or value selector  is in the form of an expression tree instead of a delegate to a method   IEnumerable lt T gt  is great for working with sequences that are iterated in-memory  but IQueryable lt T gt  allows for out-of memory things like a remote data source  such as a database or web service   Query execution   Where the execution of a query is going to be performed  quot in process quot   typically all that s required is the code  as code  to execute each part of the query   Where the execution will be performed out-of-process  the logic of the query has to be represented in data such that the LINQ provider can convert it into the appropriate form for the out-of-memory execution - whether that s an LDAP query  SQL or whatever    More in   LINQ   IEnumerable lt T gt  and IQueryable lt T gt  C  3 0 and LINQ   quot Returning IEnumerable lt T gt  vs IQueryable lt T gt  quot  Reactive Programming for  NET and C  Developers - An Introduction To IEnumerable  IQueryable  IObservable  and IQbservable 2018   quot THE MOST FUNNY INTERFACE OF THE YEAR     IQUERYABLE lt T gt  quot  from Bart De Smet

User · Answer

Here is what I wrote on a similar post  on this topic    And no  I don t usually quote myself  but these are very good articles     This article is helpful  IQueryable vs IEnumerable in LINQ-to-SQL   Quoting that article   As per the MSDN documentation  calls made on IQueryable operate by building up the internal expression tree instead   These methods that extend IQueryable Of T  do not perform any querying directly  Instead  their functionality is to build an Expression object  which is an expression tree that represents the cumulative query      Expression trees are a very important construct in C  and on the  NET platform   They are important in general  but C  makes them very useful   To better understand the difference  I recommend reading about the differences between expressions and statements in the official C  5 0 specification here  For advanced theoretical concepts that branch into lambda calculus  expressions enable support for methods as first-class objects  The difference between IQueryable and IEnumerable is centered around this point  IQueryable builds expression trees whereas IEnumerable does not  at least not in general terms for those of us who don t work in the secret labs of Microsoft   Here is another very useful article that details the differences from a push vs  pull perspective   By  push  vs   pull   I am referring to direction of data flow  Reactive Programming Techniques for  NET and C   Here is a very good article that details the differences between statement lambdas and expression lambdas and discusses the concepts of expression tress in greater depth  Revisiting C  delegates  expression trees  and lambda statements vs  lambda expressions

User · Answer

IEnumerable is refering to a collection but IQueryable is just a query and it will be generated inside a Expression Tree we will run this query to get data from database

User · Answer

First of all  IQueryable lt T gt  extends the IEnumerable lt T gt  interface  so anything you can do with a  plain  IEnumerable lt T gt   you can also do with an IQueryable lt T gt     IEnumerable lt T gt  just has a GetEnumerator   method that returns an Enumerator lt T gt  for which you can call its MoveNext   method to iterate through a sequence of T   What IQueryable lt T gt  has that IEnumerable lt T gt  doesn t are two properties in particular   one that points to a query provider  e g   a LINQ to SQL provider  and another one pointing to a query expression representing the IQueryable lt T gt  object as a runtime-traversable abstract syntax tree that can be understood by the given query provider  for the most part  you can t give a LINQ to SQL expression to a LINQ to Entities provider without an exception being thrown    The expression can simply be a constant expression of the object itself or a more complex tree of a composed set of query operators and operands  The query provider s IQueryProvider Execute   or IQueryProvider CreateQuery   methods are called with an Expression passed to it  and then either a query result or another IQueryable is returned  respectively

User · Answer

IQueryable is faster than IEnumerable if we are dealing with huge amounts of data from database because IQueryable gets only required data from database where as IEnumerable gets all the data regardless of the necessity from the database

User · Answer

In real life  if you are using a ORM like LINQ-to-SQL   If you create an IQueryable  then the query may be converted to sql and run on the database server If you create an IEnumerable  then all rows will be pulled into memory as objects before running the query    In both cases if you don t call a ToList   or ToArray   then query will be executed each time it is used  so  say  you have an IQueryable lt T gt  and you fill 4 list boxes from it  then the query will be run against the database 4 times   Also if you extent your query   q Where x name    a   ToList     Then with a IQueryable the generated SQL will contains    where name      a     but with a IEnumerable many more roles will be pulled back from the database  then the x name      a    check will be done by  NET

User · Answer

First of all  IQueryable lt T gt  extends the IEnumerable lt T gt  interface  so anything you can do with a  plain  IEnumerable lt T gt   you can also do with an IQueryable lt T gt     IEnumerable lt T gt  just has a GetEnumerator   method that returns an Enumerator lt T gt  for which you can call its MoveNext   method to iterate through a sequence of T   What IQueryable lt T gt  has that IEnumerable lt T gt  doesn t are two properties in particular   one that points to a query provider  e g   a LINQ to SQL provider  and another one pointing to a query expression representing the IQueryable lt T gt  object as a runtime-traversable abstract syntax tree that can be understood by the given query provider  for the most part  you can t give a LINQ to SQL expression to a LINQ to Entities provider without an exception being thrown    The expression can simply be a constant expression of the object itself or a more complex tree of a composed set of query operators and operands  The query provider s IQueryProvider Execute   or IQueryProvider CreateQuery   methods are called with an Expression passed to it  and then either a query result or another IQueryable is returned  respectively

User · Answer

First of all  IQueryable lt T gt  extends the IEnumerable lt T gt  interface  so anything you can do with a  plain  IEnumerable lt T gt   you can also do with an IQueryable lt T gt     IEnumerable lt T gt  just has a GetEnumerator   method that returns an Enumerator lt T gt  for which you can call its MoveNext   method to iterate through a sequence of T   What IQueryable lt T gt  has that IEnumerable lt T gt  doesn t are two properties in particular   one that points to a query provider  e g   a LINQ to SQL provider  and another one pointing to a query expression representing the IQueryable lt T gt  object as a runtime-traversable abstract syntax tree that can be understood by the given query provider  for the most part  you can t give a LINQ to SQL expression to a LINQ to Entities provider without an exception being thrown    The expression can simply be a constant expression of the object itself or a more complex tree of a composed set of query operators and operands  The query provider s IQueryProvider Execute   or IQueryProvider CreateQuery   methods are called with an Expression passed to it  and then either a query result or another IQueryable is returned  respectively

User · Answer

IEnumerable is refering to a collection but IQueryable is just a query and it will be generated inside a Expression Tree we will run this query to get data from database

User · Answer

ienumerable when we want to deal with inprocess memory  i e without dataconnection iqueryable when to deal with sql server  i e with data connection ilist   operations like add object  delete object etc

[.net] What is the difference between IQueryable<T> and IEnumerable<T>?

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