When to use First and when to use FirstOrDefault with LINQ

Question

I ve searched around and haven t really found a clear answer as to when you d want to use  First and when you d want to use  FirstOrDefault with LINQ    When would you want to use  First  Only when you d want to catch the exception if no results where returned   var result   List Where x   gt  x     foo   First     And when would you want to use  FirstOrDefault  When you d always want the default type if no result   var result   List Where x   gt  x     foo   FirstOrDefault     And for that matter  what about Take   var result   List Where x   gt  x     foo   Take 1

User · Answer

Ok let me give my two cents  First   Firstordefault are for when you use the second constructor  I won t explain what it is  but it s when you would potentially always use one because you don t want to cause an exception   person   tmp FirstOrDefault new Func lt Person  bool gt   p    gt        return string IsNullOrEmpty p Relationship

User · Answer

This type of the function belongs to element operators  Some useful element operators are defined below    First FirstOrDefault Last LastOrDefault Single SingleOrDefault   We use element operators when we need to select a single element from a sequence based on a certain condition  Here is an example     List lt int gt  items   new List lt int gt      8  5  2  4  2  6  9  2  10      First   operator returns the first element of a sequence after satisfied the condition  If no element is found then it will throw an exception   int result   items Where item    item    2  First     FirstOrDefault   operator returns the first element of a sequence after satisfied the condition  If no element is found then it will return default value of that type   int result1   items Where item    item    2  FirstOrDefault

User · Answer

I found a website that apperars to explain the need for FirstOrDefault http   thepursuitofalife com the-linq-firstordefault-method-and-null-resultsets  If there are no results to a query  and you want to to call First   or Single   to get a single row    You will get an    Sequence contains no elements    exception   Disclaimer  I have never used LINQ  so my apologies if this is way off the mark

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First of all  Take is a completely different method  It returns an IEnumerable lt T gt  and not a single T  so that s out    Between First and FirstOrDefault  you should use First when you re sure that an element exists and if it doesn t  then there s an error    By the way  if your sequence contains default T  elements  e g  null  and you need to distinguish between being empty and the first element being null  you can t use FirstOrDefault

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someList First       exception if collection is empty  someList FirstOrDefault       first item or default Type    Which one to use  It should be decided by the business logic  and not the fear of exception programm failure   For instance   If business logic says that we can not have zero transactions on any working day  Just assume   Then you should not try to handle this scenario with some smart programming  I will always use First   over such collection  and let the program fail if something else screwed up the business logic   Code   var transactionsOnWorkingDay   GetTransactionOnLatestWorkingDay    var justNeedOneToProcess   transactionsOnWorkingDay First      Not FirstOrDefault     I would like to see others comments over this

User · Answer

First will throw an exception when there are no results   FirstOrDefault won t  it will simply return either null  reference types  or the default value of the value type   e g like 0 for an int   The question here is not when you want the default type  but more  Are you willing to handle an exception or handle a default value  Since exceptions should be exceptional  FirstOrDefault is preferred when you re not sure if you re going to get results out of your query  When logically the data should be there  exception handling can be considered    Skip   and Take   are normally used when setting up paging in results   Like showing the first 10 results  and the next 10 on the next page  etc     Hope this helps

User · Answer

Others have very well described the difference between First   and FirstOrDefault    I want to take a further step in interpreting the semantics of these methods  In my opinion FirstOrDefault is being overused a lot  In the majority of the cases when you   re filtering data you would either expect to get back a collection of elements matching the logical condition or a single unique element by its unique identifier     such as a user  book  post etc    That   s why we can even get as far as saying that FirstOrDefault   is a code smell not because there is something wrong with it but because it   s being used way too often  This blog post explores the topic in details  IMO most of the times SingleOrDefault   is a much better alternative so watch out for this mistake and make sure you use the most appropriate method that clearly represents your contract and expectations

User · Answer

First      Returns first element of a sequence   It throw an error when There is no element in the result or source is null   you should use it If more than one element is expected and you want only first element    FirstOrDefault         Returns first element of a sequence   or a default value if no element is found      It throws an error Only if the source is null  you should use it  If more than one element is expected and you want only first element   Also good if result is empty    We have an UserInfos table  which have some records as shown below  On the basis of this table below I have created example       How to use First    var result   dc UserInfos First x   gt  x ID    1     There is only one record where ID   1  Should return this record ID  1 First Name  Manish Last Name  Dubey Email  xyz xyz com  var result   dc UserInfos First x   gt  x FName     Rahul         There are multiple records where FName     Rahul   First record should be return  ID  7 First Name  Rahul Last Name  Sharma Email  xyz1 xyz com  var result   dc UserInfos First x   gt  x ID   13     There is no record with ID   13  An error should be occur  InvalidOperationException  Sequence contains no elements  How to Use FirstOrDefault    var result   dc UserInfos FirstOrDefault x   gt  x ID    1     There is only one record where ID   1  Should return this record ID  1 First Name  Manish Last Name  Dubey Email  xyz xyz com  var result   dc UserInfos FirstOrDefault x   gt  x FName     Rahul      There are multiple records where FName     Rahul   First record should be return  ID  7 First Name  Rahul Last Name  Sharma Email  xyz1 xyz com  var result   dc UserInfos FirstOrDefault x   gt  x ID   13     There is no record with ID   13  The return value is null  Hope it will help you to understand when to use First   or FirstOrDefault

User · Answer

Another difference to note is that if you re debugging an application in a Production environment you might not have access to line numbers  so identifying which particular  First   statement in a method threw the exception may be difficult    The exception message will also not include any Lambda expressions you might have used which would make any problem even are harder to debug    That s why I always use FirstOrDefault   even though I know a null entry would constitute an exceptional situation   var customer   context Customers FirstOrDefault i   gt  i Id    customerId   if  customer    null       throw new Exception string Format  Can t find customer  0     customerId

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linq many ways to implement single simple query on collections  just we write joins in sql  a filter can be applied first or last depending on the need and necessity    Here is an example where we can find an element with a id in a collection  To add more on this  methods First  FirstOrDefault  would ideally return same when a collection has at least one record  If  however  a collection is okay to be empty  then First will return an exception but FirstOrDefault will return null or default  For instance  int will return 0  Thus usage of such is although said to be personal preference  but its better to use FirstOrDefault to avoid exception handling

User · Answer

First    Returns the first element of a sequence Throws exception  There are no elements in the result Use when  When more than 1 element is expected and you want only the first   FirstOrDefault     Returns the first element of a sequence  or a default value if no element is found Throws exception  Only if the source is null Use when  When more than 1 element is expected and you want only the first  Also it is ok for the result to be empty   From  http   www technicaloverload com linq-single-vs-singleordefault-vs-first-vs-firstordefault

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First    When you know that result contain more than 1 element expected and you should only the first element of sequence   FirstOrDefault    FirstOrDefault    is just like First   except that  if no element match the specified condition than it returns default value of underlying type of generic collection  It does not throw InvalidOperationException if no element found  But collection of element or a sequence is null than it throws an exception

User · Answer

I would use First   when I know or expect the sequence to have at least one element  In other words  when it is an exceptional occurrence that the sequence is empty   Use FirstOrDefault   when you know that you will need to check whether there was an element or not  In other words  when it is legal for the sequence to be empty  You should not rely on exception handling for the check   It is bad practice and might hurt performance    Finally  the difference between First   and Take 1  is that First   returns the element itself  while Take 1  returns a sequence of elements that contains exactly one element

User · Answer

First   will throw an exception if there s no row to be returned  while  FirstOrDefault   will return the default value  NULL for all reference types  instead   So if you re prepared and willing to handle a possible exception   First   is fine  If you prefer to check the return value for    null anyway  then  FirstOrDefault   is your better choice   But I guess it s a bit of a personal preference  too  Use whichever makes more sense to you and fits your coding style better

[c#] When to use .First and when to use .FirstOrDefault with LINQ?

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