Calling 'Read' when the data reader is closed is not a valid operation error using Entity Framework database first approach - asp.net-web-api

Question

I am creating a Web API that will fetch information from a table using Entity Framework database-first approach using stored procedures. ListAllTeams_Result is the complex type object created in Entity Framework. I am looping through the import function GetAllTeams() and populating the complex type. I am getting an error in my business layer when trying to access the data access layer
The error that I am getting is the following code
var team = _teamRepository.GetAllTeams();
The result of the query cannot be enumerated more than once.
Note: this error is in the inner stack and doesn't stop the application from executing
foreach (var t in team)
Calling 'Read' when the data reader is closed is not a valid operation.
Note : This stops execution
Business Layer
public IEnumerable<TeamDto> GetTeam()
{
var team = _teamRepository.GetAllTeams();
if (team != null)
{
foreach (var t in team.ToList())
{
yield return Mapper.Map<TeamDto>(t);
}
}
yield break;
}
DataAccess layer:
public IEnumerable<ListAllTeams_Result> GetAllTeams()
{
using (var mcrContext = new MCREntities())
{
return (from team in mcrContext.ListAllTeams("")
select new ListAllTeams_Result
{
TeamID = team.TeamID,
TeamDescription = team.TeamDescription,
CountryCode = team.CountryCode,
CreatedBy = team.CreatedBy,
CreatedDate = team.CreatedDate,
ModifiedBy = team.ModifiedBy,
ModifiedDate = team.ModifiedDate
});
}
}

Answer 1

I have found what the problem is. I had to add ToList in the return
using (var mcrContext = new MCREntities())
{
return (from team in mcrContext.ListAllTeams("")
select new ListAllTeams_Result
{
TeamID = team.TeamID,
TeamName = team.TeamName,
TeamDescription = team.TeamDescription,
CountryCode = team.CountryCode,
CreatedBy = team.CreatedBy,
CreatedDate = team.CreatedDate,
ModifiedBy = team.ModifiedBy,
ModifiedDate = team.ModifiedDate
}).ToList();
}