Entity Framework - Create navigation property

Question

i created a db-model with the entity framework wizzard in Visual Studio. There are 2 tables (job, stocktype) which are related to each other with the table stocktype2job.

enter image description here

Job <------- no direct relation / navigation property --------> StockType
 |                                                                  |
 |                                                                  |
 ---------------------> StockType2Job ----------------------------->

With a Job Object, i could do something like this ...

EntitiesObject db = new EntitiesObject();
Job job = db.Jobs.SingleOrDefault(j => j.IdJob == 40);

List<StockType> stockTypes = new List<StockType>;
foreach (StockType2Job st2j in job.StockType2Jobs)
    {
        stockTypes.add(st2j.StockType);
    }

That should work just fine. But is there a way to create a navigation property in the job entity so i can write something like this?

EntitiesObject db = new EntitiesObject();
Job job = db.Jobs.SingleOrDefault(j => j.IdJob == 40);

List<StockType> stockTypes = job.StockTypes; // <<-----

Thanks for your kind Help Apo

Gert Arnold · Accepted Answer · 2012-12-14 12:55:25Z

2

It is clear (from the self reference) that StockType2Jobs does not only contain foreign keys to StockType and Job, so you can't map a many-many relationship with a navigation property job.StockTypes. So you can't do anything else then collecting StockType via job.StockType2Jobs. But that's not a big deal:

List<StockType> stockTypes = job.StockType2Jobs.Select(x => x.StockType);

You might get tempted to wrap this in an unmapped property job.StockTypes, but usually it's not a good idea to do this.

answered Dec 14, 2012 at 12:55

Gert Arnold

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Morvader · Accepted Answer · 2012-12-14 11:13:25Z

1

Try something like this:

 var stocksTypes = from st in db.StockType 
     from stj in st.StockType2Job where stj.Job.IdJob==40 select st;

This code is not creating any new navigation property, it just "joining" the tables. I supose that the StockType2Jobs table exists for a good reason.

I recommend you to have a look at how to deal with N to N relationship with EF.

Some links [1] [2]

Hope Helps

edited Dec 14, 2012 at 11:13

answered Dec 14, 2012 at 10:53

Morvader

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1 Comment

Simon Rossmann Over a year ago

no doubt that this would work but i rather dont want to use linq when there is a more elegant way, but thx anyway!

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