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POMany-to-many relationships using EF Code First
 

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  1. POMany-to-many relationships using EF Code First
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    <p>I have two classes defined as such:</p> <pre><code>public class Questionnaire { public int QuestionnaireID { get; set; } public string Title { get; set; } public bool Active { get; set; } public virtual ICollection&lt;Question&gt; Questions { get; set; } public virtual ICollection&lt;Vendor&gt; Vendors { get; set; } } public class Vendor { public int VendorID { get; set; } public string VendorName { get; set; } public virtual ICollection&lt;Questionnaire&gt; OpenQuestionnaires { get; set; } public virtual ICollection&lt;Questionnaire&gt; SubmittedQuestionnaires { get; set; } public virtual ICollection&lt;QuestionnaireUser&gt; QuestionnaireUsers { get; set; } } </code></pre> <p>I beleive this is the correct way to establish a many-to-many relationship between these classes, and when the project is built, I would expect three tables to be created.</p> <p>However, when I attempt to to relate one Questionnaire to two different Vendors, I receive the following error when attempting to save the changes (context.SaveChanges()):</p> <p>*Multiplicity constraint violated. The role 'Vendor_OpenQuestionnaires_Source' of the relationship 'QuestionnaireApp.Models.Vendor_OpenQuestionnaires' has multiplicity 1 or 0..1.*</p> <p>If I assign a Questionnaire to only one Vendor, save the changes and then assign it to another and again save changes I no longer get the error; however the Questionaire is then related only to the last Vendor to which it was assigned, indicating that (at best) there is a one-to-many relationship being created.</p> <p>I'm hoping that there is something wrong with the way I'm declaring the many-to-many relationship between these classes, or perhaps there is something I need to add to the context class to "encourage" the relationsip, but perhaps many-to-many relationships like this are not supported, or cannot be created using "Code First"?</p> <p>Thank you for your time,</p> <p>Jason</p>
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    1. USjasongullickson
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      1. USCiaran Bruen
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    1. COI am unfamiliar with either technology you're using, but in SQL to make a many to many relationship you need a bridging table which has a one to many with both tables and therefore aggregates the many to many. I do not see such a structure in your design..
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      1. USJimmy Hoffa
    2. COI think you need to tell EF explicitly that's a many-to-many relationship where it boot straps EF.
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      1. USChris Marisic
    3. COIn general, if you have the ICollection<T> for the corresponding child collection in each parent object, EF will automiatically generate the intervening briding table for you based on convention. The EF Model hides the intervening table.
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      1. USJim Wooley
 

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