Generic Repository pattern

-Generic Repository Pattern in CSharp.md

Creating a Generic Repository Pattern

The below example shows how to implement a Repository of objects in a generic fashion. This was adapted and simplified from this article: https://code.msdn.microsoft.com/generic-repository-pattern-ddea2262

Overview

The point of this code is to allow the generic access to any object type in the datastore without the need to define a repository for each object. It is important to note that, although the below examples should work as is, it is recommended to make use of a dependency injection framework as database connection limits are not considered.

EFRepository.cs

using LinqKit;
using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Linq.Expressions;

public class EFRepository<T> : IRepository<T> where T : class
{
  protected DbContext Context;
  protected readonly DbSet<T> Table;
  
  public EFRepository(DbContext context)
  {
    Context = context;
    Table = Context.Set<T>();
  }
  
  public IEnumerable<T> Get(Expression<Func<T, bool>> searchCriteria = null)
  {
    return searchCriteria == null ? Table.ToList() : Table.Where(searchCriteria).ToList();
  }
  
  public ResultPage<T> GetByPage<TKey>(Expression<Func<T, bool>> searchCriteria, Expression<Func<T, TKey>> orderCriteria, bool orderDescending, int pageNumber, int recordsPerPage)
  {
    // 1. Search for rows (AsExpandable used as sub-queries do not play nice with LINQ to SQL. See here: http://tomasp.net/blog/linq-expand.aspx
    var rawResults = searchCriteria == null ? Table : Table.AsExpandable().Where(searchCriteria);
    
    // 2. Apply ordering
    if (orderDescending)
    {
      rawResults = rawResults.OrderByDescending(orderCriteria);
    }
    else
    {
      rawResults = rawResults.OrderBy(orderCriteria);
    }
    
    // 3. Skip and take pages
    var resultingRows = rawResults.Skip((pageNumber - 1) * recordsPerPage).Take(recordsPerPage);
    
    // 4. Return results
    return new ResultPage<T>(resultingRows, rawResults.Count(), resultingRows.Count());
  }
  
  public T GetByKey(object key)
  {
    return Table.Find(key);
  }
  
  public virtual void Add(T record)
  {
    Table.Add(record);
  }
  
  public virtual void AddMany(IEnumerable<T> records)
  {
    Table.AddRange(records);
  }
  
  public virtual void Update(T record)
  {
    Table.Attach(record);
    Context.Entry(record).State = EntityState.Modified;
  }
  
  public void Remove(object key)
  {
    var record = Table.Find(key);
    Table.Remove(record);
  }
  
  public void RemoveMany(IEnumerable<T> records)
  {
    Table.RemoveRange(records);
  }
  
  public void RemoveAll()
  {
    Table.RemoveRange(Table);
  }
  
  public virtual void Commit()
  {
    Context.SaveChanges();
  }
  
  public int RowCount(Expression<Func<T, bool>> filterCriteria = null)
  {
    if (filterCriteria == null) filterCriteria = t => true;
    return Table.Count(filterCriteria);
  }
  
  public void Dispose()
  {
    Context.Dispose();
  }
}

IRepository.cs

using System;
using System.Collections.Generic;
using System.Linq.Expressions;

public interface IRepository<T> : IDisposable where T : class
{
  // Returns number of rows where the criteria matches
  int RowCount(Expression<Func<T, bool>> filterCriteria = null);

  // Retrieves records based on criteria
  IEnumerable<T> Get(Expression<Func<T, bool>> searchCriteria = null);
  
  // Retrieves subset of records based on criteria
  ResultPage<T> GetByPage<TKey>(Expression<Func<T, bool>> searchCriteria, Expression<Func<T, TKey>> orderCriteria, bool orderDescending, int pageNumber, int recordsPerPage);
  // Retrieves single record based on unique key
  T GetByKey(object key);

  // Adds record to table
  void Add(T record);
  // Adds many records to table
  void AddMany(IEnumerable<T> records);

  // Updates object
  void Update(T record);

  // Removes single Object
  void Remove(object key);
  // Removes many objects
  void RemoveMany(IEnumerable<T> records);
  // Removes all objects
  void RemoveAll();

  // Updates all changed objects
  void Commit();
}

ResultPage.cs

using System.Collections.Generic;
using System.Runtime.Serialization;

[DataContract]
public class ResultPage<T> where T : class
{
  public ResultPage(IEnumerable<T> result, long? totalRecords, long? returnedRecords)
  {
      TotalRecords = totalRecords;
      ReturnedRecords = returnedRecords;
      Results = result;
  }

  public ResultPage() : this(null, null, null)
  {

  }

  [DataMember(Name = "results")]
  public IEnumerable<T> Results { get; }
  
  [DataMember(Name = "totalRecords")]
  public long? TotalRecords { get; }
  
  [DataMember(Name = "returnedRecords")]
  public long? ReturnedRecords { get; }
}

UserService.cs

// A few examples of how to use the generic repository
// Note that you probably would want to do all of this using a DI framework...

public class UserService
{
  private readonly IRepository<User> _userRepository;
  
  public UserService()
  {
    // Ideally use Dependency Injection; If you have many inter-dependent services / modules, you will start running out of available DB connections
    _userRepository = new EFRepository<User>(new MyDatabaseContext());
  }
  
  public List<UserDto> GetUsers()
  {
    return _userRepository.Get();
  }
  
  public UserDto CreateUser(UserDto toCreate)
  {
    var newUser = new User();
    newUser.FirstName = toCreate.FirstName;
    newUser.LastName = toCreate.LastName;
    newUser.UserName = toCreate.UserName;
    
    _userRepository.Add(newUser);
    _userRepository.Commit();
    
    return newUser;
  }
  
  public UserDto UpdateUser(UserDto toUpdate)
  {
    var entity = _userRepository.GetByKey(toUpdate.Id);
    if (entity != null)
    {
      entity.FirstName = toUpdate.FirstName;
      entity.LastName = toUpdate.LastName;
      entity.UserName = toUpdate.UserName;

      _userRepository.Update(entity);
      _userRepository.Commit();
    }
    return null;
  }
  
  public void RemoveUser(int userId)
  {
    _userRepository.Remove(userId);
    _userRepository.Commit();
  }
}