MySQL Net连接器问题

Question

I am using the MySQL Net Connector (http://dev.mysql.com/downloads/connector/net/) and I have imported the MySQL database into Visual Studio (ADO.NET Entity Data Model) and created the relations.

I now want to Collect some data from the database into my custom Business Entity and have coded the routing as follows:

public List<Property> GetProperties()
{
    using (ncsEntities dataContext = this.ncsDataContext)
    {

        // Begin Test #1
        var q1 = from p in dataContext.ra_properties.Top("3")
                 where p.street_id > 0
                 select p;

        List<ra_properties> list1 = q1.ToList();
        // End Test #1   list2 is populated as expected
        // The property ra_streets is populated and is not null


        // Begin Test #2
        var q2 = from p in dataContext.ra_properties.Top("3")
                 where p.street_id > 0
                 select new Property
                 {
                     Key2 = p.valuation_id,
                     Address = "Some Dummy Value"
                 };

        List<Property> list2 = q2.ToList();
        // End Test #2
        // list2 is populated as expected.


        // Begin Test #3
        var q3 = from p in dataContext.ra_properties.Top("3")
                 where p.street_id > 0
                 select new Property
                 {
                     Key2 = p.valuation_id,
                     Address = (p.ra_streets == null || p.ra_streets.address_1 == null) ? string.Empty : p.ra_streets.address_1
                 };

        List<Property> list3 = q3.ToList();
        // End Test #3
        // This Test Fails.  The exception message is
        // Object reference not set to an instance of an object.

        return list3;

    }
}

I can not figure out why the last Test does not work. It fails with the exception message Object reference not set to an instance of an object. Can anyone help me out here?

Answer 1

I think you need to add explicit reference to ra_streets in your query. I cannot test it at the moment but it seems like it is the case.

Try to change it to

// Begin Test #3
var q3 = from p in dataContext.ra_properties.Include("ra_streets").Top("3")
         where p.street_id > 0
         select new Property
         {
             Key2 = p.valuation_id,
             Address = (p.ra_streets == null || p.ra_streets.address_1 == null) ? string.Empty : p.ra_streets.address_1
         };

and see if it works?