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POHierarchical POCO objects & Repositories
 

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  1. POHierarchical POCO objects & Repositories
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    <p>Suppose I have a domain model that has 1:1 correspondence to the physical model. Also:</p> <ul> <li>all the tables in the physical model has the column name 'Id' as a primary key</li> <li>Many of the tables have 'LastChanged' timestamp column</li> <li>Some of the tables contain localized data</li> </ul> <p><strong>Objective</strong>: create domain model classes (POCO) and appropriate repositories. Tools - VS2010, EF4.1</p> <p>The <em>most obvious</em> approach to take is to generate EF model from the DB and then run T4 POCO Generator over it. The output is a set of POCO classes.</p> <pre class="lang-cs prettyprint-override"><code>//POCO classes public class Country { public int Id { get; set; } public string Name { get; set; } public DateTime LastModified { get; set; } ... } public class User { public int Id { get; set; } public string FirtsName { get; set; } public DateTime LastModified { get; set; } ... } </code></pre> <p>So far so good but we come across some code duplications when implementing repositories. Both on the interface definition level:</p> <pre class="lang-cs prettyprint-override"><code>public interface ICountryRepository { IEnumerable&lt;Country&gt; FindAll(); Country FindById(int id); void Add(Country country); void Delete(Country country); } //Here the ONLY difference is the type of the entity public interface IUserRepository { IEnumerable&lt;User&gt; FindAll(); User FindById(int id); void Add(User user); void Delete(User user); } </code></pre> <p>And on the implementation level:</p> <pre class="lang-cs prettyprint-override"><code>class CountryRepository : ICountryRepository { IEnumerable&lt;Country&gt; FindAll() { //implementation } Country FindById(int id) { //find by id logic } void Add(Country country) { //logic } void Delete(Country country) { //logic } } class UserRepository : IUserRepository { IEnumerable&lt;User&gt; FindAll() { //the only difference in the implementation //is the type of returned entity } User FindById(int id) { //the only difference in the implementation //is the type of returned entity } void Add(User user) { //the only difference in the implementation //is the type of returned entity } void Delete(User user) { //the only difference in the implementation //is the type of returned entity } } </code></pre> <p>Taking into account that <strong>most of the code above can be written more generically</strong>, we can also take the following approach.</p> <p>Create a POCO objects hierarchy:</p> <pre class="lang-cs prettyprint-override"><code>public class EntityBase { public int Id { get; set; } } public class TrackableEntity : EntityBase { public DateTime LastChanged { get; set; } } public class LocalizedEntity : TrackableEntity { public int ResourceId { get; set; } } public class Country : LocalizedEntity { } </code></pre> <p>And then repository hierarchy with a base implemetation:</p> <pre class="lang-cs prettyprint-override"><code>public interface IRepository&lt;TEntity&gt; where TEntity : EntityBase { IEnumerable&lt;TEntity&gt; FindAll(); TEntity FindById(int id); void Add(TEntity entity); void Delete(TEntity entity); } public interface ILocalizedRepository&lt;TEntity&gt; : IRepository&lt;TEntity&gt; where TEntity : LocalizedEntity { IEnumerable&lt;TEntity&gt; FindByCultureIso2(string cultureIso2); } public interface ICountryRepository : ILocalizedRepository&lt;Country&gt; { } internal class RepositoryBase&lt;TEntity&gt; : IRepository&lt;TEntity&gt; where TEntity : EntityBase { private readonly IObjectSet&lt;TEntity&gt; _objectSet; public RepositoryBase(ObjectContext database) { _objectSet = database.CreateObjectSet&lt;TEntity&gt;(); } protected virtual IQueryable&lt;TEntity&gt; All() { return _objectSet; } public virtual IEnumerable&lt;TEntity&gt; FindAll() { return All().ToList(); } public virtual TEntity FindById(int id) { return All().Where(entity =&gt; entity.Id == id).SingleOrDefault(); } public virtual void Add(TEntity entity) { _objectSet.AddObject(entity); } public virtual void Delete(TEntity entity) { _objectSet.DeleteObject(entity); } } internal class LocalizedRepositoryBase&lt;TEntity&gt; : RepositoryBase&lt;TEntity&gt;, ILocalizedRepository&lt;TEntity&gt; where TEntity : LocalizedEntity { public LocalizedRepositoryBase(ObjectContext database) : base(database) { } protected override IQueryable&lt;TEntity&gt; All() { return (base.All() as ObjectSet&lt;TEntity&gt;).Include("Resource.LocalizedResources.Culture"); } public IEnumerable&lt;TEntity&gt; FindByCultureIso2(string cultureIso2) { IEnumerable&lt;TEntity&gt; entities = All().Where(...); return entities.ToList(); } } internal class CountryRepository : LocalizedRepositoryBase&lt;Country&gt;, ICountryRepository { public CountryRepository(ObjectContext database) : base(database) { } } </code></pre> <p>The compelling advantage of the latter approach is that the code is much more structured which allows to avoid code duplication. </p> <p>But this scenario is hardly amenable to T4 code gen which opens up a surface for a large amount of manual work.</p> <p>I would appreciate if you let me know you thinking on the following:</p> <ul> <li>How do you think, is the beauty of the code really worth the trouble of implementing it manually?</li> <li>Is there any other ways to get rid of the code duplication?</li> </ul>
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    1. USay.metallo
    1. USay.metallo
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    1. COYou are a developer = you are responsible for writing a code and that is exactly what you did! If you want to generate code live with code duplication.
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      1. USLadislav Mrnka
    2. COThat's a good point ;) But sometimes there is just code that I'd prefer not to write manually - no complex/business logic at all, DTOs, proxies, etc. I don't think anyone would disagree that those are best done with some tools.
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      1. USay.metallo
    3. CORepository is specific thing. Correct repository implementation has specific methods per entities so you cannot generate it.
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      1. USLadislav Mrnka
 

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