/// <summary>
/// Visits a <see cref="TakeOperator" /> node.
/// </summary>
/// <param name="op">Node to visit.</param>
/// <returns>Result of visiting the node.</returns>
protected internal override QueryOperator VisitTake(TakeOperator op)
{
var src = VisitAndConvert <MonadMember>(op.Source);
var count = Visit(op.Count);
if (src != op.Source || count != op.Count)
{
return(MakeTake(op, src, count));
}
return(op);
}
/// <summary>
/// Visits a <see cref="TakeOperator" /> operator 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 VisitTake(TakeOperator op)
{
var source = VisitAndConvert <MonadMember>(op.Source);
var count = Visit(op.Count);
// Take coalescing
var srcOperator = source.QueryNodeType == QueryNodeType.Operator ? (QueryOperator)source : null;
var srcTake = srcOperator != null && srcOperator.NodeType == OperatorType.Take ? (TakeOperator)srcOperator : null;
if (srcTake != null)
{
if (TryExtractNullaryLambdaBody(count, out Expression count1) &&
count1.NodeType == ExpressionType.Constant &&
TryExtractNullaryLambdaBody(srcTake.Count, out Expression count2) &&
count2.NodeType == ExpressionType.Constant)
{
var c1 = (int)((ConstantExpression)count1).Value;
var c2 = (int)((ConstantExpression)count2).Value;
return(op.QueryExpressionFactory.Take(
op.ElementType,
srcTake.Source,
DefaultQueryExpressionFactory.Instance.LambdaAbstraction(
Expression.Lambda(
Expression.Constant(
Math.Min(c1, c2)
)
),
Array.Empty <QueryTree>()
)
));
}
var p1 = Expression.Parameter(typeof(int));
var p2 = Expression.Parameter(typeof(int));
return(op.QueryExpressionFactory.Take(
op.ElementType,
srcTake.Source,
DefaultQueryExpressionFactory.Instance.LambdaAbstraction(
Expression.Lambda(
Expression.Call(s_Min, p1, p2),
p1,
p2
),
new[] { srcTake.Count, count }
)
));
}
return(op.Update(source, count));
}
/// <summary>
/// Makes a <see cref="TakeOperator" /> with the given children.
/// </summary>
/// <param name="node">Original query expression.</param>
/// <param name="source">Source query expression.</param>
/// <param name="count">Count query expression.</param>
/// <returns>Representation of the original query expression.</returns>
protected sealed override QueryOperator MakeTake(TakeOperator node, MonadMember source, QueryTree count)
{
return(node.QueryExpressionFactory.Take(node.ElementType, source, count));
}
/// <summary>
/// Creates a textual representation of the TakeOperator with the given children.
/// </summary>
/// <param name="node">Original query expression.</param>
/// <param name="source">Source query expression.</param>
/// <param name="count">Count query expression.</param>
/// <returns>Representation of the original query expression.</returns>
protected override string MakeTake(TakeOperator node, string source, string count)
{
return(string.Format(CultureInfo.InvariantCulture, "@Take({0}, {1})", source, count));
}
/// <summary>
/// Makes a <see cref="TakeOperator" /> with the given children.
/// </summary>
/// <param name="node">Original query expression.</param>
/// <param name="source">Source query expression.</param>
/// <param name="elementType">Element type for the resulting operator.</param>
/// <param name="count">Count query expression.</param>
/// <returns>Representation of the original query expression.</returns>
protected virtual QueryOperator MakeTake(TakeOperator node, Type elementType, MonadMember source, QueryTree count)
{
return(node.QueryExpressionFactory.Take(elementType, source, count));
}
