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    <p>@Alex - i know this is an old question, but what I would be doing would be letting the Repository do <em>really simple stuff</em> only. This means, get all records for a table or view.</p> <p>Then, in the SERVICES layer (you are using an n-tiered solution, right? :) ) i would be handling all the 'special' query stuff there.</p> <p>Ok, example time.</p> <h3>Repository Layer</h3> <pre><code>ContactRepository.cs public IQueryable&lt;Contact&gt; GetContacts() { return (from q in SqlContext.Contacts select q).AsQueryable(); } </code></pre> <p>Nice and simple. <code>SqlContext</code> is the instance of your <code>EF Context</code> .. which has an <code>Entity</code> on it called <code>Contacts</code> .. which is basically your sql Contacts class.</p> <p>This means, that method basically is doing: <code>SELECT * FROM CONTACTS</code> ... but it's not hitting the database with that query .. it's only a query right now.</p> <p>Ok .. next layer.. <strong><em>KICK</em></strong> ... up we go (<em>Inception</em> anyone?)</p> <h3>Services Layer</h3> <pre><code>ContactService.cs public ICollection&lt;Contact&gt; FindContacts(string name) { return FindContacts(name, null) } public ICollection&lt;Contact&gt; FindContacts(string name, int? year) { IQueryable&lt;Contact&gt; query = _contactRepository.GetContacts(); if (!string.IsNullOrEmpty(name)) { query = from q in query where q.FirstName.StartsWith(name) select q; } if (int.HasValue) { query = from q in query where q.Birthday.Year &lt;= year.Value select q); } return (from q in query select q).ToList(); } </code></pre> <p>Done.</p> <p>So lets recap. First, we start our with a simple '<em>Get everything from contacts</em>' query. Now, if we have a name provided, lets add a filter to filter all contacts by name. Next, if we have a year provided, then we filter the birthday by Year. Etc. Finally, we then hit the DB (with this modified query) and see what results we get back.</p> <p>NOTES:-</p> <ul> <li>I've omitted any Dependency Injection for simplicity. It's more than highly recommended.</li> <li>This is all pseduo-code. Untested (against a compiler) but you get the idea ....</li> </ul> <h3>Takeaway points</h3> <ul> <li>The Services layer handles all the smarts. That is where you decide what data you require.</li> <li>The Repository is a simple SELECT * FROM TABLE or a simple INSERT/UPDATE into TABLE.</li> </ul> <p>Good luck :)</p>
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    1. COI think it is worth mentioning that this really only works efficiently, and please correct me if I am wrong, if you are using a DAL that supports deferred execution such as Linq To Sql as per your example. Otherwise you will retrieve a lot of data from your data store that may not get used. Now if you know the user is going to be using the same data set in multiple different ways this ultimately may be ok, but if they are just running this query once then retrieving entirely unrelated data this design would lead to mentionable overhead.
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    2. COWe've all done this hack. For each additional filter we add an 'optional' parameter. I think the authors original example is far cleaner and easier to use (and reuse).
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    3. CO@joshlrogers : dude - waaaay incorrect! DO you know what an IQueryable is/does? it doesn't hit the DB. It's a _query_. So i'm not really doing a SELECT * FROM XXX. I *extend* that query by adding extra where clauses .. when required. So the final sql is actually a SELECT * FROM XXX WHERE blah (if the user has provided the *optional* name and/or *optional* year arguments*. So unless I misunderstood you .. careful what you say :(
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