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POMultiplicity constraint violated. The role xxx of the relationship xxx has multiplicity 1 or 0..1
 

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  1. POMultiplicity constraint violated. The role xxx of the relationship xxx has multiplicity 1 or 0..1
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    <p>Ive seen this question asked a few times but I'm afraid I am just not understanding the answers.</p> <p>In a nutshell, I have a Player that contains a property of type PlayerBaseballStat. Its a 1 to 1 relationship. PlayerBaseballStat has an <code>ICollection&lt;BaseballStat&gt;</code> property. both PlayerBaseballStat and BaseballStat have PlayerId to join the relationships. </p> <pre><code> public class Player { public Player() { // initialize with empty shell PlayerBaseballStat = new PlayerBaseballStat(); } public int PlayerId { get; set; } //other properties removed for brevity public virtual PlayerBaseballStat PlayerBaseballStat { get; set; } } public class PlayerBaseballStat { [Required, Key, DatabaseGenerated(DatabaseGeneratedOption.None)] public int PlayerId { get; set; } public virtual Player Player { get; set; } //other properties removed for brevity public virtual ICollection&lt;BaseballStat&gt; BaseballStats { get; set; } } public class BaseballStat : EntityBase { public int PlayerId { get; set; } public virtual Player Player { get; set; } public int Year { get; set; } [MaxLength(25)] [Required] public string StatName { get; set; } [Required] public decimal StatValue { get; set; } } </code></pre> <p>The mappings are:</p> <pre><code> modelBuilder.Entity&lt;Player&gt;() .HasOptional(p =&gt; p.PlayerBaseballStat); modelBuilder.Entity&lt;PlayerBaseballStat&gt;() .HasRequired&lt;Player&gt;(x =&gt; x.Player); modelBuilder.Entity&lt;PlayerBaseballStat&gt;() .HasMany(p =&gt; p.BaseballStats); modelBuilder.Entity&lt;BaseballStat&gt;() .HasKey(x =&gt; new { x.PlayerId, x.Year, x.StatName }); modelBuilder.Entity&lt;BaseballStat&gt;() .HasRequired(x =&gt; x.Player); </code></pre> <p>The data access layer is a templated repository. The multiplicity constraint violation occurs on a read operation.</p> <pre><code>public T Get(Expression&lt;Func&lt;T, bool&gt;&gt; where) { return dbset.Where(where).FirstOrDefault&lt;T&gt;(); } </code></pre> <p>The actual read is</p> <pre><code>_playerBaseballStatsRepository.Get(x =&gt; x.PlayerId == playerId); </code></pre> <p>That translates to</p> <pre><code>dataContext.PlayerBaseballStats.FirstOrDefault(x =&gt; x.PlayerId == playerId); </code></pre> <p>I know I am missing something in the mappings but I just cannot seem to figure it out. Please help.</p>
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