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PONeed some help sorting out a major abstract pattern headache within my DAL
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  1. PONeed some help sorting out a major abstract pattern headache within my DAL
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    copied!<p>I've caused myself a bit of an issue with my Data Access Layer. In this particular instance, I have a table that contains potentially 5 types of 'entity'. These are basically Company, Customer, Site, etc. The type is dictated by a PositionTypeId within the table. They're all in the same table as they all havethe same data structure; <em>PositionId, Description and Code</em>.</p> <p>I have a main abstract class as follows:</p> <pre><code>public abstract class PositionProvider&lt;T&gt; : DalProvider&lt;T&gt;, IDalProvider where T : IPositionEntity { public static PositionProvider&lt;T&gt; Instance { get { if (_instance == null) { // Create an instance based on the current database type } return _instance; } } private static PositionProvider&lt;T&gt; _instance; public PositionType PositionType { get { return _positionType; } } private PositionType _positionType; // Gets a list of entities based on the PositionType enum's value. public abstract List&lt;T&gt; GetList(); internal void SetPositionType(RP_PositionType positionType) { _positionType = positionType; } } </code></pre> <p>I want to then be able to put all the general code within an inherting class that is either SQL or Oracle based. This is my SQL implementation:</p> <pre><code>public class SqlPositionProvider&lt;T&gt; : PositionProvider&lt;T&gt; where T : IPositionEntity { public override List&lt;T&gt; GetList() { int positionTypeId = (int)this.PositionType; using (SqlConnection cn = new SqlConnection(Globals.Instance.ConnectionString)) { SqlCommand cmd = new SqlCommand("Get_PositionListByPositionTypeId", cn); cmd.Parameters.Add("@PositionTypeId", SqlDbType.Int).Value = positionTypeId; cmd.CommandType = CommandType.StoredProcedure; cn.Open(); return this.GetCollectionFromReader(this.ExecuteReader(cmd)); } } } </code></pre> <p>I've then create a class for each type as follows (this is the CustomerProvider as an example):</p> <pre><code>public class CustomerProvider { public static PositionProvider&lt;CustomerEntity&gt; Instance { get { if ((int)PositionProvider&lt;CustomerEntity&gt;.Instance.PositionType == 0) { PositionProvider&lt;CustomerEntity&gt;.Instance.SetPositionType(PositionType.Customer); } return PositionProvider&lt;CustomerEntity&gt;.Instance; } } } </code></pre> <p>This all works fantastically... until I realised that I have certain functions that are related specifically to certain position types. I.e. I need to be able to get all Customers (which is an IPositionType) based on the user permissions.</p> <p>So I need to add another abstract method:</p> <pre><code>public abstract List&lt;CustomerEntity&gt; GetCustomersByUserPermission(Guid userId); </code></pre> <p>Now, obviously I don't want this within my PositionProvider abstract class as that would mean that method would appear when dealing with the site/company provider.</p> <p>How can I add this, and other, additional methods without having to duplicate the code within the SqlPositionProvider?</p> <p><strong>Edit:</strong></p> <p>The only idea I've come up with is to separate the PositionProvider out into a common property of the CustomerProvider, SiteProvider, etcProvider:</p> <pre><code>public abstract class CustomerProvider { public CustomerProvider() { this.Common.SetPositionType(PositionType.Customer); } public PositionProvider&lt;CustomerEntity&gt; Common { get { if (_common == null) { DalHelper.CreateInstance&lt;PositionProvider&lt;CustomerEntity&gt;&gt;(out _common); } return _common; } } private PositionProvider&lt;CustomerEntity&gt; _common; public static CustomerProvider Instance { get { if (_instance == null) { DalHelper.CreateInstance&lt;CustomerProvider&gt;(out _instance); } return _instance; } } private static CustomerProvider _instance; public abstract List&lt;CustomerEntity&gt; GetCustomersByUserPermission(Guid userId); } </code></pre> <p>This would allow me to put the specific code within <code>CustomerProvider.Instance.MyNonGenericMethod()</code>, and then to access the <code>PositionProvider</code> I could do <code>CustomerProvider.Instance.Common.GetList()</code>... This does seem like a bit of a hack though.</p>
 

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