Multiplicity constraint violation debug

Question

I'm getting a multiplicity constraint violation in my entity model.

On my entity model I have two relationship properties:

SubstanceTypeMixConstituents
Category

SubstanceTypeMixConstituents
- Multiplicity * (Many)
Category
- Multiplicity: 1 (One)
- Foreign key, not null

enter image description here

How do I find what causing the problem and resolve this issue?

System.InvalidOperationException: A relationship multiplicity constraint violation occurred: An EntityReference expected at least one related object, but the query returned no related objects from the data store. at System.Data.Objects.DataClasses.EntityReference`1.Load(MergeOption mergeOption) at System.Data.Objects.DataClasses.RelatedEnd.DeferredLoad() at System.Data.Objects.Internal.LazyLoadBehavior.LoadProperty[TItem](TItem propertyValue, String relationshipName, String targetRoleName, Boolean mustBeNull, Object wrapperObject) at System.Data.Objects.Internal.LazyLoadBehavior.<>c__DisplayClass7`2.<GetInterceptorDelegate>b__2(TProxy proxy, TItem item) at System.Data.Entity.DynamicProxies.SubstanceType_BEE32ACA75386E981F7CA3F6A3C565BC1D8ADACA228C603A2EACC918DCDCBA30.get_Category()

@Michael - you lost me here: I have a multiplicity constraint on one releationship of 1 (One) where the database has a foreign key that are not null and a second relationship of * (Many) where the database has a many to many relationship. Do you have a one-to-many or many-to-many relationship? — Yakimych
– Yakimych, Commented May 3, 2011 at 11:54
Sorry. I have edited the post in order to make more sense. Hope it helps. — Michael
– Michael, Commented May 3, 2011 at 13:42
@Michael - a screenshot of your model would be best, but as far as I understand, you have two entities - Category and SubstanceTypeMixConstituent which have a One-to-many relationship - a Category can have multiple SubstanceTypeMixConstituents, but a SubstanceTypeMixConstituent can have (and must have) only one Category (correct me if I am wrong). The error message you get means exactly what it says - you are either trying to save a Category with an empty collection of SubstanceTypeMixConstituents, or a SubstanceTypeMixConstituent without a Category. — Yakimych
– Yakimych, Commented May 3, 2011 at 14:03
@Yakimych: Put the part: SubstanceTypeMixConstituent without Category as an answer because it will be the problem. — Ladislav Mrnka
– Ladislav Mrnka, Commented May 3, 2011 at 14:08
@Ladislav - How do you figure it's not the other way around though? — Yakimych
– Yakimych, Commented May 3, 2011 at 14:13

Yakimych · Accepted Answer · 2011-05-03 14:20:08Z

As far as I understand, you have two entities - Category and SubstanceTypeMixConstituent which have a One-to-many relationship - a Category can have multiple SubstanceTypeMixConstituents, but a SubstanceTypeMixConstituent can have (and must have) only one Category (correct me if I am wrong). The error message you get means exactly what it says - you are either trying to save a Category with an empty collection of SubstanceTypeMixConstituents, or a SubstanceTypeMixConstituent without a Category.

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Multiplicity constraint violation debug

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