LINQ Pocket Reference: Learn and Implement LINQ for .NET Applications (Pocket Reference (O'Reilly)) by Joseph Albahari & Ben Albahari

Author:Joseph Albahari & Ben Albahari [Albahari, Joseph]
Language: eng
Format: epub
Tags: COMPUTERS / Programming Languages / Visual BASIC
ISBN: 9780596558390
Publisher: O'Reilly Media
Published: 2008-02-25T18:30:00+00:00

Joining in lambda syntax

The following comprehension syntax join:

from c in customers join p in purchases on c.ID equals p.CustomerID select new { c.Name, p.Description, p.Price };

in lambda syntax is as follows:

customers.Join ( // outer collection purchases, // inner collection c => c.ID, // outer key selector p => p.CustomerID, // inner key selector (c, p) => new // result selector { c.Name, p.Description, p.Price } );

The result selector expression at the end creates each element in the output sequence. If you have additional clauses prior to projecting, such as orderby in this example:

from c in customers join p in purchases on c.ID equals p.CustomerID orderby p.Price select c.Name + " bought a " + p.Description;

you must manufacture a temporary anonymous type in the result selector in lambda syntax. This keeps both c and p in scope following the join:

customers.Join ( // outer collection purchases, // inner collection c => c.ID, // outer key selector p => p.CustomerID, // inner key selector (c, p) => new { c, p } ) // result selector .OrderBy (x => x.p.Price) .Select (x => x.c.Name + " bought a " + x.p.Description);

Comprehension syntax is usually preferable when joining; it’s less fiddly.

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