如何使用Entity Framework从通过外键链接的多个表中获取所有数据？

Question

I'm new to Entity Framework and I'm having trouble to fetch all data from the following database:

I created controllers for all of the entities shown above like this:

    // Retrieve entire DB
    AareonAPIDBEntities dbProducts = new AareonAPIDBEntities();

    // Get all customers
    [System.Web.Http.AcceptVerbs("GET")]
    [System.Web.Http.HttpGet]
    [System.Web.Http.Route("customer")]
    public IEnumerable<Customer> Default()
    {
        List<Customer> customers = dbProducts.Customers.ToList();
        return customers;
    }

    //Get customer by ID
    [System.Web.Http.AcceptVerbs("GET")]
    [System.Web.Http.HttpGet]
    [System.Web.Http.Route("customer/{id}")]
    public Customer getById(int id = -1)
    {
        Customer t = dbProducts.Customers
                               .Where(h => h.customerID == id)
                               .FirstOrDefault();
        return t;
    }

Now I'm having trouble finding out how to retrieve all of the database data linked by foreign keys in table PropertyLeaseContract by customerID . I'm trying to get a JSON response where I get the customersID and values, therein an array of objects from the linked LeaseContract and Property .

Hope someone can help.

Thanks in advance!

Answer 1

Assuming your relations are properly set up in the DbContext Configuration and you have appropriate Navigation Properties in your Entity Classes it should work something like this:

public Customer getById(int id = -1)
{
    Customer t = dbProducts.Customers
            .Where(h => h.customerID == id)
            .Include(x => x.PropertyLeaseContracts)
              .ThenInclude(x => x.LeaseContract)
            .Include(x => x.PropertyLeaseContracts)
              .ThenInclude(x => x.Property)
            .FirstOrDefault();
    return t;
}

For that to work your Customer Class needs to have a Collection Property of PropertyLeaseContract and be setup as a OneToMany Relation. And your PropertyLeaseContract class needs to have Properties of type LeaseContract and Property and also be setup correctly.

EDIT: The above code works only in Entity Framework Core as mentioned by @TanvirArjel. In Entity Framework Full code should look something like this:

public Customer getById(int id = -1)
{
    Customer t = dbProducts.Customers
            .Where(h => h.customerID == id)
            .Include(x => x.PropertyLeaseContracts.Select(plc => plc.LeaseContract))
            .Include(x => x.PropertyLeaseContracts.Select(plc => plc.Property))
            .FirstOrDefault();
    return t;
}