/// <summary>
/// Visits a <see cref="FirstOperator" /> and coalesces it with any possible child operators.
/// </summary>
/// <param name="op">The operator to visit.</param>
/// <returns>The coalesced operator.</returns>
protected internal override QueryOperator VisitFirst(FirstOperator op)
{
var source = VisitAndConvert <MonadMember>(op.Source);
if (source.QueryNodeType == QueryNodeType.Operator)
{
var sourceOp = (QueryOperator)source;
if (sourceOp.NodeType == OperatorType.Where)
{
var where = (WhereOperator)sourceOp;
if (op.ElementType == where.ElementType) // new C[0].Where<B>(_ => B.b).First<A>() can't be optimized
{
return(op.QueryExpressionFactory.First(
op.ElementType,
where.Source,
where.Predicate));
}
}
}
return(op.Update(source));
}
/// <summary>
/// Makes a <see cref="FirstOperator" /> with the given children.
/// </summary>
/// <param name="node">Original query expression.</param>
/// <param name="source">Source query expression.</param>
/// <returns>Representation of the original query expression.</returns>
protected sealed override QueryOperator MakeFirst(FirstOperator node, MonadMember source)
{
return(node.QueryExpressionFactory.First(node.ElementType, source));
}
/// <summary>
/// Creates a textual representation of the FirstOperator with the given children.
/// </summary>
/// <param name="node">Original query expression.</param>
/// <param name="source">Source query expression.</param>
/// <returns>Representation of the original query expression.</returns>
protected override string MakeFirst(FirstOperator node, string source)
{
return(string.Format(CultureInfo.InvariantCulture, "@First({0})", source));
}
/// <summary>
/// Makes a <see cref="FirstOperator" /> with the given children.
/// </summary>
/// <param name="node">Original query expression.</param>
/// <param name="elementType">Element type for the resulting operator.</param>
/// <param name="source">Source query expression.</param>
/// <returns>Representation of the original query expression.</returns>
protected virtual QueryOperator MakeFirst(FirstOperator node, Type elementType, MonadMember source)
{
return(node.QueryExpressionFactory.First(elementType, source));
}