Understanding LINQ in One-Liners

Here I will provide one liner-explanations of terminology used with LINQ.

• From: initialize a data source just like we declare a variable first before using it in C#.
• where: applies a condition in a LINQ query.
• select: selects a value from the LINQ query.
• var: assigns a variable for when we don't know the return type of our LINQ query.
• Deffered execution: the LINQ query will store only the information, it will not provide the result directly to you. To get the result you need to use a foreach loop or toList or ToArray method. Until this stage LINQ is in the deffered execution stage.
• foreach loop: to iterate the result that we got from the LINQ query and then to execute the result.
• IEnumerable: use this if you know that your LINQ query return type will be a string and the data is in your in-memory.
• IQueryable: use this if the query is generated using a database.
• Lambda expression: use the => operator if you are using a method-based LINQ query. The left hand of the => operator is the input and the right hand side is the output.
• Expression lambda: use an expression lambda if you want to pass an expression on the left hand side of the => operator.
• Statement lambda: If you want to use a statement in the right hand side of the => operator then use the statement lambda enclosed in brackets {}.
• Async Lambda: use this if you want to use async or await in your LINQ query.
• Async and await: to do asynchronous programming like if one resource is busy then the other program will keep executing, it will not wait for completion of the resource task.
• let: use the let keyword when you want to store the result of any expression inside the LINQ.
• LINQ to SQL: use this if you want to access a collection from a SQL Server in your in-memory.
• System.Data.Linq.dll: add this DLL if you want LINQ to SQL.
• insertonsubmit: use this when you want to insert data into SQL using LINQ to SQL.
• deleteonsubmit: use this when you want to delete data in SQL using LINQ to SQL.
• submitchanges: use this in LINQ to SQL after insertonsubmit or deleteonsubmit or if you have updated any data in your in-memory collection. This will submit your data finally to the database.
• LINQ to dataset: use this if you want to query your in-memory dataset.
• System.Data.DataSetExtensions: use this DLL if you want to use LINQ to a dataset.
• asenumerable: use this if you want to apply LINQ to a datatable since a datatable doesn't implement ienumerable or iqueryable.
• field: use the field method in LINQ to access a datatable column using LINQ to dataset.
• setfield: use SetField if you want to set column values in a DataRow using LINQ to dataset.
• isnull: use isnull if you want to check that a column is null or not using LINQ to dataset.
• join: use this if you want to join two datatables using LINQ to dataset.
• groupjoin: use this when you want a superset of inner joins and left outer joins.
• LINQ to Objects: use this if you want to apply the LINQ on an array, list or dictionary.
• LINQ to XML: use this if you want to do manipulation with XML or if you want to create new XML using LINQ.
• Distinct: use this with your LINQ query if you want to remove duplicate values from a collection.
• Except: use this with LINQ if you want to return the set difference of two collections.
• Intersect: use this if you want to return common data from two collections in LINQ.
• Union: use this when you want all elements from both collections but the result should not contain duplicate data.
• All: use this in LINQ if you want to check that your condition is satisfying all the elements of a collection.
• Any: use this in LINQ if you want to check your condition with any element in a collection.
• Contains: use this if you want to check whether or not a sequence contains a specified element.
• Skip: use this if you want to skip elements up to a specified position in a sequence.
• SkipWhile: use this if you want to skip elements until the condition is true.
• Take: use this if you want to take the first n elements from a sequence.
• Takewhile: use this if want to take all the elements when the condition becomes true.
• concat: use this if you want to combine two sequences, it may contain duplicate values also.
• AsQueryable: use this if you want to convert a generic Ienumerable type to a generic IQueryable Type.
• Cast: use this if you want to cast an element of a sequence in any other type.
• ToArray: use this if you want to convert your collection into an array and if you want to force query execution.
• ToDictionary: use this function if you want to put your element into a dictionary based on key. This will also force query execution.
• ToList: use this if you want to convert collections into a generic list. This will also force query execution.
• ToLookup: this is also like a dictionary but with a one-to-many relationship. Use this if you want to put your element into a dictionary.

Refer: http://www.c-sharpcorner.com/UploadFile/3dc6f6/linq-understanding-in-one-liner/