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POWhat 'possible data inconsistency' is entity framework worried about in a 'foreign key participating in multiple relationships' situation?
 

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  1. POWhat 'possible data inconsistency' is entity framework worried about in a 'foreign key participating in multiple relationships' situation?
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    <p>Suppose the following database schema:</p> <pre><code>Table A: AId (PK) Table B: BId (PK) Table C: CId (PK) Table AB: AId, BId (composite PK, FKs to A and B), Data Table BC: BId, CId (composite PK, FKs to B and C), Data Table ABC: AId, BId, CId, Data </code></pre> <p>In the database, <code>ABC</code> has two FKs: one to <code>AB</code> on <code>AId</code> and <code>BId</code>, and one to <code>BC</code> on <code>BId</code> and <code>CId</code>.</p> <p>Use the EF Designer and attempt to create a Model from this database.</p> <p>If you have <code>Include foreign key columns in the model</code> <em>checked</em>, it works; but having FK Columns in the model isn't very nice.</p> <p>If you have <code>Include foreign key columns in the model</code> <em>unchecked</em>, only one of the FKs from <code>ABC</code> will be successfully mapped. To see what went wrong, <a href="https://stackoverflow.com/questions/543971/ado-net-entity-framework-update-wizard-will-not-add-tables/546077#546077">you have to view the <code>.edmx</code> xml (thanks Craig!)</a> and you see this error:</p> <blockquote> <p>warning 6037: Foreign key constraint 'FK_ABC_BC' has been omitted from the storage model. Column 'BId' of table 'Model.Store.ABC' is a foreign key participating in multiple relationships. A one-to-one Entity Model will not validate since data inconsistency is possible.</p> </blockquote> <p>I've read <a href="https://stackoverflow.com/questions/582742">the only other mention of this problem I can find on SO</a>, and I don't think this is the same problem. I can't see anything wrong at a <em>database design</em> level. I'm going to work round this for the time being by imposing surrogate keys on <code>AB</code> and <code>BC</code>, but what I'd really like to know is:</p> <p><strong>What possible data inconsistency is EF worried about happening here, if it created a model to match the database?</strong></p> <p>And is there anything I can do to persuade it that everything's going to be OK?</p>
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