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.