Why EF navigation property return null?

Same behavior, but different root cause than selected answer:

Navigation property can also be null if you turned off myContext.Configuration.AutoDetectChangesEnabled

Very obvious, but this got me when I was implementing some performance improvments.

Check this out: Navigation Property With Code First . It mentions about why navigation property is null and the solutions of it.

By default, navigation properties are null, they are not loaded by default. For loading navigation property, we use “include” method of IQuearable and this type of loading is called Eager loading.

Eager loading: It is a process by which a query for one type of entity loads the related entities as a part of query and it is achieved by “include” method of IQueryable.

Try this:

DbContext.Configuration.ProxyCreationEnabled = true;    
DbContext.Configuration.LazyLoadingEnabled = true;  

If DbContext.Configuration.ProxyCreationEnabled is set to false, DbContext will not load child objects for some parent object unless Include method is called on parent object. Setting DbContext.Configuration.LazyLoadingEnabled to true or false will have no impact on its behaviours.

If DbContext.Configuration.ProxyCreationEnabled is set to true, child objects will be loaded automatically, and DbContext.Configuration.LazyLoadingEnabled value will control when child objects are loaded.

I think this is problem:

Edit: 3) Are you sure there is data in your database and that the foreign key from Indicator to IndicatorGroup has a value for that specific record? I am saying this because the value "null" is valid if there is simply no data.

P.S. If you do not see a foreign key on Indicator called "IndicatorGroupId", there might be an "IndicatorId" on the table "IndicatorGroup", in which case - going from the names you provided - your database is misconfigured and you will need to use fluent syntax or data attributes to instruct EF on how to make the foreign keys.

Try to this and make sure foreign key is corrected.

public class CalculationType
{
    public long ID { get; set; }
    public string UnitName { get; set; }
    public int Point { get; set; }
    public DateTime DateCreated { get; set; }
    public DateTime DateChanged { get; set; }
    [ForeignKey("IndicatorID")]
    public string IndicatorId { get; set; } //this is the foreign key, i saw in your database is: Indicator_ID, avoid this, rename it to IndicatorID or IndicatorId

    public virtual Indicator Indicator { get; set; }
    public virtual IList<Сalculation> Calculations { get; set; }
}

1) Is Lazy Loading enabled? If not, you need to explicitly load your navigation properties with the '.Include' syntax.

2) Are you sure EF should be able to detect that relation? Did you use Code First or Database First?

Edit: 3) Are you sure there is data in your database and that the foreign key from Indicator to IndicatorGroup has a value for that specific record? I am saying this because the value "null" is valid if there is simply no data.

P.S. If you do not see a foreign key on Indicator called "IndicatorGroupId", there might be an "IndicatorId" on the table "IndicatorGroup", in which case - going from the names you provided - your database is misconfigured and you will need to use fluent syntax or data attributes to instruct EF on how to make the foreign keys.