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POHow to implement Repository Pattern with interface, base and concrete
 

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  1. POHow to implement Repository Pattern with interface, base and concrete
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    <p>I have almost completed implementing my repository pattern by having a <code>IRepository&lt;T&gt;</code> interface, a <code>NewsRepository</code> class and a <code>News</code> entity. The problem I ran into was trying to abstract out common methods to a base Repository class. </p> <p>I could not find a way to abstract the Get method in the <code>NewsRepository</code> as it contains a specific Linq expression.</p> <p><strong>My questions are</strong>:</p> <p><strong>1)</strong> How do I abstract to a base class the <code>public T Get(int id)</code> method please? The only way I have done it so far is by passing in <code>Expression&lt;Func&lt;T,bool&gt;&gt;</code> instead of an int, but then that deosn't really abstract out common behaviour as each sub-class will still need to pass in an expression that is almost identical in each case ie <code>n =&gt; n.id == id</code>.</p> <p><strong>2)</strong> How do I pass into the base class on the Update method the sub-class GetViolations and map methods please? I imagine the solution is possibly by using delegates, but I couldn't get the syntax to compile</p> <p>This is a simplified set of the code - in practice I have a Save method which does Update and Insert rather than just the Update shown here.</p> <pre><code>public interface IRepository&lt;T&gt; { T Get(int id); void Update(T item); } public class NewsRepository : IRepository&lt;News&gt; { private Table&lt;News&gt; _newsTable; public NewsRepository(string connectionString) { _newsTable = new DataContext(connectionString).GetTable&lt;News&gt;(); } public News Get(int id) { return _newsTable.SingleOrDefault(n =&gt; n.NewsId == id); } public void Update(News item) { var errors = item.GetRuleViolations(); if (errors.Count &gt; 0) throw new RuleException(errors); News dbNews = _newsTable.SingleOrDefault(n =&gt; n.NewsId == item.NewsId); map(dbNews, item); _newsTable.Context.SubmitChanges(); } private void map(News dbNews, News news) { dbNews.Title = news.Title; dbNews.Article = news.Article; } } public class Repository&lt;T&gt; where T : class { protected Table&lt;T&gt; _table; public Repository(Table&lt;T&gt; t) { _table = t; } //How do i do this??! - This doesn't compile due to T no having a NewsId public T Get(int id) { return _table.SingleOrDefault(n =&gt; n.NewsId == id); } //This seems to be a solution, but it's not really abstracting common behaviour as each //sub-class will still need to pass in the same linq expression... public T Get(Expression&lt;Func&lt;T,bool&gt;&gt; ex) { return _table.SingleOrDefault(ex); } public void Update(T item) { //How is it possible to pass in the GetRuleViolations and map functions to this method? var errors = item.GetRuleViolations(); if (errors.Count &gt; 0) throw new RuleException(errors); T dbNews = _table.SingleOrDefault(n =&gt; n.NewsId == item.NewsId); map(dbNews, item); _table.Context.SubmitChanges(); } } </code></pre>
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