/// <summary>
/// Resolves the deduplicated entity.
/// </summary>
/// <param name="entity">The entity to deduplicate.</param>
/// <param name="primaryKey">The primary key of the entity.</param>
/// <returns>The deduplicated entity.</returns>
protected virtual TEntityType Deduplicate(TEntityType entity, object primaryKey)
{
if (KeyCache.ContainsKey(primaryKey))
{
return(KeyCache[primaryKey]);
}
return(entity);
}
/// <summary>
/// Maps a row of data to an entity.
/// </summary>
/// <param name="context">A context that contains information used to map Dapper objects.</param>
/// <returns>The mapped entity, or null if the entity has previously been returned.</returns>
public virtual TEntityType Map(EntityMapContext context)
{
if (PrimaryKey == null)
{
throw new InvalidOperationException("PrimaryKey selector is not defined, but is required to use DeduplicatingEntityMapper.");
}
// Deduplicate the top object (entity) in the list
if (context.Items != null &&
context.Items.Any())
{
if (context.Items.First() is TEntityType entity)
{
var previous = entity;
var primaryKey = PrimaryKey(entity);
if (primaryKey == null)
{
throw new InvalidOperationException("A null primary key was provided, which results in an unpredictable state.");
}
// Deduplicate the entity using available information
entity = Deduplicate(entity, primaryKey);
if (!object.ReferenceEquals(previous, entity))
{
context.Items = new[] { entity }.Concat(context.Items.Skip(1));
}
// Map the object
var next = Mapper.Map(context);
// Return null if we are returning a duplicate object.
// Queries can filter out null entries to prevent duplicates.
if (ReturnsNullWithDuplicates && KeyCache.ContainsKey(primaryKey))
{
return(null);
}
// Cache a reference to the entity
KeyCache[primaryKey] = next;
// And, return it
return(next);
}
}
return(default(TEntityType));
}