Eager Loading In Repository Pattern Entity Framework Core

In this blog, we will learn Eager Loading In Repository Pattern Entity Framework Core

Introduction

 

Eager loading is the process whereby a query for one type of entity also loads related entities as part of the query, so that we don't need to execute a separate query for related entities.

 

In simple language, Eager loading joins the entities which have foreign relation and returns the data in a single query.

 

Now, the question is how to properly handle the eager-loading problem for complex object graphs within the Repository pattern.

 

Let's get started.

 

Step 1:  Add a method into your Interface which eager loads the entities which we specify:

public interface IProjectInterface<T> where T : class
{
Task<IEnumerable<T>> EntityWithEagerLoad(Expression<Func<T, bool>> filter,                string[] children);
Task<List<T>> GetModel();
T GetModelById(int modelId);
Task<bool> InsertModel(T model);
Task<bool> UpdateModel(T model);
Task<bool> DeleteModel(int modelId);
void Save();
}

The method EntityWithEagerLoad() takes 2 arguments, one is filter criteria and another is an array of entities which we want to eager load.

 

Step 2: Define the method EntityWithEagerLoad in your base repository:

public async Task<IEnumerable<T>> EntityWithEagerLoad(Expression<Func<T, bool>> filter, string[] children)
{
            try
            {
                IQueryable<T> query = dbEntity;
                foreach (string entity in children)
                {
                    query = query.Include(entity);

                }
                return await query.Where(filter).ToListAsync();
            }
            catch(Exception e)
            {
                throw e;
            }

Step 3 : For using this method , call this function from your controller as shown  below:

[HttpGet]
       [Route("api/Employee/getDetails/{id}")]
       public async Task<IEnumerable<string>> GetDetails([FromRoute]int id)
       {
           try
           {
      var children = new string[] { "Address", “Education” };

      var employeeDetails=await _repository.EntityWithEagerLoad (d => d.employeeId==id,
      children);

           }
           catch(Exception e)
           {
               Throw e;
           }

The variable employeeDetails contains employee details with their Address and education details.