Question

I’m not sure if this is possible but I am inserting a lot of entities into the database, and for each item it has say a language property which is an entity. Currently I create a new language object for each item that is being inserted but this is just for testing as it creates a lot of duplicates. The languages should be unique in the database and should just point to an existing language record, the only way I can think of is to do seperate service calls for every insert to lookup a language code and get the id of the existing language which is a lot of overhead.

Is there a way for it to automatically lookup a record based on the language code and use that record?

Thanks

Answer 1

Both ObjectContext and DbContext have methods that try to find an already loaded entity from the context in memory – GetObjectByKey for ObjectContext and Find for DbContext. Using these methods you avoid to load a Language entity more than once from the database.

Both methods need a primary key value as input parameter to lookup the entity by key. Essentially think of these methods as accessing an internal dictionary that relates the primary key to the entity object.

Now, refering to your comment…

Essentially trying to match on a custom value rather than the
id/primary key value.

…you can’t use these methods because they rely on knowing the primary key value you want to lookup.

What I would do is to mimic the logic of the mentioned internal dictionary by your own dictionary that relates your “custom value” to the entity instead of the primary key. I assume that the custom value is unique in the Language table.

So, the idea would be:

Given you have entities like this…

public class MyEntity
{
    public int Id { get; set; }
    public Language Language { get; set; }
    public string SomeOtherValue { get; set; }
    // ... more
}

public class Language
{
    public int Id { get; set; }             // primary key value
    public string CustomValue { get; set; } // the unique custom value
    // ... more
}

…and you have a collection of data you are using to insert the new entities…

public class Data
{
    public string SomeOtherValue { get; set; }
    public string LanguageCustomValue { get; set; }
    // ... more
}

var dataList = new List<Data>
{
    new Data { SomeOtherValue = "A", LanguageCustomValue = "EN" },
    new Data { SomeOtherValue = "B", LanguageCustomValue = "FR" },
    new Data { SomeOtherValue = "C", LanguageCustomValue = "EN" },
    new Data { SomeOtherValue = "D", LanguageCustomValue = "EN" },
    // ... more
}

…then you could use this:

using (var context = new MyContext())
{
    var dict = new Dictionary<string, Language>();
    foreach (var data in dataList)
    {
        Language language;
        if (!dict.TryGetValue(data.LanguageCustomValue, out language))
        {
            // load the language only once from the database
            language = context.Languages.SingleOrDefault(l =>
                l.CustomValue == data.LanguageCustomValue);
            dict.Add(data.LanguageCustomValue, language);
        }

        var myEntity = new MyEntity
        {
            SomeOtherValue = data.SomeOtherValue,
            Language = language
        };

        context.MyEntities.Add(myEntity);  // or AddObject
    }
    context.SaveChanges();
}

This would load only one Language entity per LanguageCustomValue, do this only once and doesn’t create duplicates of Language objects in the database.