/// <summary>
/// Combines the first expression with the second using the specified merge function.
/// </summary>
/// <param name="first">The first expression.</param>
/// <param name="second">The second expression.</param>
/// <param name="merge">The merge function.</param>
/// <typeparam name="T">Element type.</typeparam>
private static Expression <T> Compose <T>(
[NotNull] this Expression <T> first,
[NotNull] Expression <T> second,
[NotNull] Func <Expression, Expression, Expression> merge)
{
var map = first.Parameters
.Select((f, i) => new { f, s = second.Parameters[i] })
.ToDictionary(p => p.s, p => (Expression)p.f);
var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
/// <inheritdoc />
public Expression <Func <TEntity, bool> > Where <TEntity, TInput>(
[NotNull] Expression <Func <TEntity, TInput, bool> > predicate,
TInput input)
{
if (IgnoreDefaults && Equals(input, default(TInput)))
{
return(null);
}
if (IgnoreDefaults && input is IEnumerable enumerable)
{
var enumerator = enumerable.GetEnumerator();
var disposable = enumerator as IDisposable;
try
{
if (!enumerator.MoveNext())
{
return(null);
}
}
finally
{
disposable?.Dispose();
}
}
if (typeof(TInput) == typeof(string))
{
return(StringWhere(predicate as Expression <Func <TEntity, string, bool> >, input as string));
}
var replacement = new Dictionary <ParameterExpression, Expression>
{
{ predicate.Parameters.Last(), Expression.Constant(input, typeof(TInput)) }
};
var body = ParameterRebinder.ReplaceParameters(
replacement,
predicate.Body);
var filter = Expression.Lambda <Func <TEntity, bool> >(
body,
predicate.Parameters.First());
return(filter);
}
/// <inheritdoc cref="Where{TEntity,TInput}"/>
private Expression <Func <TEntity, bool> > StringWhere <TEntity>(
[NotNull] Expression <Func <TEntity, string, bool> > predicate,
string input)
{
if (IgnoreDefaults && string.IsNullOrWhiteSpace(input))
{
return(null);
}
var replacement = new Dictionary <ParameterExpression, Expression>
{
{ predicate.Parameters.Last(), Expression.Constant(ToLower(input), typeof(string)) }
};
var body = ParameterRebinder.ReplaceParameters(
replacement,
predicate.Body);
var filter = Expression.Lambda <Func <TEntity, bool> >(
body,
predicate.Parameters.First());
return(filter);
}