Collections Namespace. IList is useful when you want to Add or remove items from the list. IList can find out the no of elements in the collection without iterating the collection. IList supports deferred execution.
IList doesn't support further filtering. IEnumerable IEnumerable exists in System. IEnumerable is best to query data from in-memory collections like List, Array etc.
IEnumerable doesn't support add or remove items from the list. Using IEnumerable we can find out the no of elements in the collection after iterating the collection. Thank you very much, Ehsan. Unfortunately, Pluralsight did change the URL structure without having a redirect for older links to the new location. I fixed the link pointing to the C Interfaces course in the article above.
IEnumerable First of all, it is important to understand, that there are two different interfaces defined in the. I just want to let you know about the official description from the msdn documentation: Defines size, enumerators, and synchronization methods for all nongeneric collections. IList The IList interface has of course a non-generic and a generic version. Conclusion Take a look at the following graphic. Which type should you depend on? The following table gives you an overview of how you can decide which type you should depend on.
You only need read-only access to that collection. Recommendation If you are now curious about interfaces, how they work, how to implement them on your own and how their use can improve your design and therefore the quality of your entire code base, I highly recommend watching C Interfaces by Jeremy Clark on Pluralsight.
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Related Questions. How to get IEnumerable list ordered alfabetical? Simple IEnumerator use with example. There is no viewdata item of ienumerable error? Again though, just don't worry about it until you really care about ensuring a LINQ query doesn't get executed twice or require it executed in a certain order relative to other code, at which point assign your variable to itself.
ToList to force execution and you'll be fine. By the time the "Process Data" loop is reached, the query may no longer by valid. For example, if the query is being run on a DataContext that has already been Disposed, your code will throw an exception. This kind of thing becomes very confusing when you are processing a query in a different context than where you created it. A secondary issue is that your connection will not be released until the "Process Data" loop completes.
This is only a problem if "Process Data" is complex. A connection typically remains open until you consume the query results. If you expect to take time to process all the results and are not opposed to caching the results, apply ToList to the query.
So, these issues are why you are being encouraged to ensure that the query is actually executed, e. As a general rule, I recommend avoiding iterating over an IEnumerable more than once. Assuming consumers of your code follow this rule, I don't consider it a concern that someone might hit the database twice by executing the query twice.
Another benefit of enumerating the IEnumerable early is exceptions will be thrown at the appropriate location. This assists debugging. For example, if you got a deadlock exception inside one of your Razor views, it wouldn't really be as clear as if the exception occurred during one of your data access methods.
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