public IQueryable <TDerivedEntity> SatisfiedBy <TDerivedEntity>(IQueryable <TDerivedEntity> entities)
where TDerivedEntity : TEntity
{
if (entities == null)
{
throw new ArgumentNullException(nameof(entities));
}
var entityPredicate = Predicate;
if (entityPredicate == null)
{
throw new InvalidOperationException("Predicate");
}
if (typeof(TDerivedEntity) == typeof(TEntity))
{
return((IQueryable <TDerivedEntity>)((IQueryable <TEntity>)entities).Where(entityPredicate));
}
var entityParameter = entityPredicate.Parameters.Single();
var derivedEntityParameter = Expression.Parameter(typeof(TDerivedEntity), entityParameter.Name);
var parameterVisitor = new ParameterVisitor(entityParameter, derivedEntityParameter);
var derivedEntityBody = parameterVisitor.Visit(entityPredicate.Body);
var derivedEntityExpression = Expression.Lambda(derivedEntityBody, derivedEntityParameter);
return(entities.Where((Expression <Func <TDerivedEntity, bool> >)derivedEntityExpression));
}
private static Expression <Func <TDerivedEntity, bool> > Compose <TEntity, TDerivedEntity>(
this Expression <Func <TEntity, bool> > firstExpression,
Expression <Func <TDerivedEntity, bool> > secondExpression,
Func <Expression, Expression, Expression> mergeFunc)
where TDerivedEntity : TEntity
{
var derivedParameter = Expression.Parameter(typeof(TDerivedEntity));
var firstParameter = firstExpression.Parameters.Single();
var firstParameterVisitor = new ParameterVisitor(firstParameter, derivedParameter);
var firstBody = firstParameterVisitor.Visit(firstExpression.Body);
var secondParameter = secondExpression.Parameters.Single();
var secondParameterVisitor = new ParameterVisitor(secondParameter, derivedParameter);
var secondBody = secondParameterVisitor.Visit(secondExpression.Body);
return(Expression.Lambda <Func <TDerivedEntity, bool> >(
mergeFunc(firstBody, secondBody), derivedParameter));
}