What is possible multiple enumeration of IEnumerable?
Deferred Danger. One of the many useful warnings in ReSharper is “Possible multiple enumeration of IEnumerable“. If you enumerate an enumerable more than once, ReSharper detects that and warns you about it. Although this warning may seem pointless at first, there are two good reasons to pay attention to it.
Why is multiple enumeration bad?
The enumeration result is not calculated once and cached like Lazy. If the enumeration operation itself is expansive, for example, query into the database, multiple enumerations would be harmful to the performance of the program. If the enumeration operation has side effects, multiple enumerations might result in bugs.
How do you know if an IEnumerable is empty?
“check if ienumerable is empty c#” Code Answer
- IEnumerable enumerable = new List();
- if(! enumerable. Any())
- {
- throw new InvalidOperationException();
- }
Is IEnumerable deferred execution?
You can implement deferred execution for your custom extension methods for IEnumerable using the yield keyword of C#. For example, you can implement custom extension method GetTeenAgerStudents for IEnumerable that returns a list of all students who are teenagers.
Can an IEnumerable be null?
The returned IEnumerable<> might be empty, but it will never be null .
How do I get a count of IEnumerable?
IEnumerable has not Count function or property. To get this, you can store count variable (with foreach, for example) or solve using Linq to get count.
What is LINQ IEnumerable?
IEnumerable is best to query data from in-memory collections like List, Array, etc. While query data from a database, 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 LINQ to Object and LINQ to XML queries.
Why is LINQ lazy?
Yes, LINQ uses lazy evaluation. The database would be queried when the foreach starts to execute, but it would fetch all the data in one go (it would be much less efficient to do millions of queries for just one result at a time).
What is LINQ materialization?
Materializing LINQ Queries Once When writing LINQ queries using IEnumerable or IQueryable interfaces, developers can materialize (call ToList , ToArray or similar methods) or not to materialize queries immediately (Lazy loading). The lack of materialization allows developers to work with collections lazily.
Does enumerate count IEnumerable?
Count(…) does enumerate the collection. If you’re running into the problem where you can’t iterate through a collection twice, try this: List myList = dataContext.
How do I count IEnumerable in C#?
In its simplest form (without any parameters), the Count() method returns an int indicating the number of elements in the source sequence. IEnumerable strings = new List { “first”, “then”, “and then”, “finally” }; // Will return 4 int result = strings. Count();
Can we use LINQ with IEnumerable?
Yes it can. You just need to use the Cast function to get it converted to a typed IEnumerable .
When to use IEnumerable?
Distinct – Gets only the unique items in the list
How can I do select unique with LINQ?
What is LINQ Distinct Method in C#?
How to get index using LINQ?
What about LINQ to SQL, I am trying to use the same concept using a database table, but it doesn’t work for me. For example: var resultado = DB.Orders.Select((orden, index) => new { Index=index,Orden=orden.Employee }); GridView1.DataSource = resultado; GridView1.DataBind(); I getting this error:
How to use LINQ to select into an object?
Examples. The following code example demonstrates how to use Select (IEnumerable ,Func ) to project over a sequence of values.