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//---------------------------------------------------------------------
// <copyright file="OrderByLifter.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//
// @owner Microsoft
//---------------------------------------------------------------------
namespace System.Data.Objects.ELinq
{
using System.Data.Common.CommandTrees;
using System.Data.Common.CommandTrees.ExpressionBuilder;
using System.Data.Common.Utils;
using System.Data.Metadata.Edm;
using System.Diagnostics;
internal sealed partial class ExpressionConverter
{
/// <summary>
/// A context-sensitive DbExpression builder class that simulates order preservation
/// for operators (project, filter, oftype, skip and limit) that are not natively order
/// preserving. The builder simulates order preservation by 'lifting' order keys in
/// the expression tree. For instance, source.Sort(o).Where(f) is rewritten as
/// source.Where(f).Sort(o) since otherwise the sort keys would be ignored.
///
/// In general, the lifter works as follows:
///
/// - The input to the operator is matched against a series of patterns for intrinsically
/// ordered expressions.
/// - For each pattern, the lifter encodes the compensation required for each of the
/// lifting operators that can be applied.
/// </summary>
private sealed class OrderByLifter
{
private readonly AliasGenerator _aliasGenerator;
internal OrderByLifter(AliasGenerator aliasGenerator)
{
_aliasGenerator = aliasGenerator;
}
#region 'Public' builder methods.
internal DbExpression Project(DbExpressionBinding input, DbExpression projection)
{
OrderByLifterBase lifter = GetLifter(input.Expression);
return lifter.Project(input.Project(projection));
}
internal DbExpression Filter(DbExpressionBinding input, DbExpression predicate)
{
OrderByLifterBase lifter = GetLifter(input.Expression);
return lifter.Filter(input.Filter(predicate));
}
internal DbExpression OfType(DbExpression argument, TypeUsage type)
{
OrderByLifterBase lifter = GetLifter(argument);
return lifter.OfType(type);
}
internal DbExpression Skip(DbExpressionBinding input, DbExpression skipCount)
{
OrderByLifterBase lifter = GetLifter(input.Expression);
return lifter.Skip(skipCount);
}
internal DbExpression Limit(DbExpression argument, DbExpression limit)
{
OrderByLifterBase lifter = GetLifter(argument);
return lifter.Limit(limit);
}
#endregion
private OrderByLifterBase GetLifter(DbExpression root)
{
return OrderByLifterBase.GetLifter(root, _aliasGenerator);
}
private abstract class OrderByLifterBase
{
protected readonly DbExpression _root;
protected readonly AliasGenerator _aliasGenerator;
protected OrderByLifterBase(DbExpression root, AliasGenerator aliasGenerator)
{
_root = root;
_aliasGenerator = aliasGenerator;
}
/// <summary>
/// Returns a lifter instance which supports lifting the intrinsic order of the given
/// source expression across specific operations (filter, project, oftype, skip, and limit)
/// </summary>
/// <remarks>
/// Lifting only occurs for expressions that are ordered. Each of the nested
/// OrderByLifterBase class implementations represents one or two of the ordered patterns with
/// the exception of the PassthroughOrderByLifter. The latter class represents expressions
/// without intrinsic order that therefore require no lifting.
/// </remarks>
internal static OrderByLifterBase GetLifter(DbExpression source, AliasGenerator aliasGenerator)
{
if (source.ExpressionKind == DbExpressionKind.Sort)
{
return new SortLifter((DbSortExpression)source, aliasGenerator);
}
if (source.ExpressionKind == DbExpressionKind.Project)
{
var project = (DbProjectExpression)source;
DbExpression projectInput = project.Input.Expression;
if (projectInput.ExpressionKind == DbExpressionKind.Sort)
{
return new ProjectSortLifter(project, (DbSortExpression)projectInput, aliasGenerator);
}
if (projectInput.ExpressionKind == DbExpressionKind.Skip)
{
return new ProjectSkipLifter(project, (DbSkipExpression)projectInput, aliasGenerator);
}
if (projectInput.ExpressionKind == DbExpressionKind.Limit)
{
var limit = (DbLimitExpression)projectInput;
DbExpression limitInput = limit.Argument;
if (limitInput.ExpressionKind == DbExpressionKind.Sort)
{
return new ProjectLimitSortLifter(project, limit, (DbSortExpression)limitInput, aliasGenerator);
}
if (limitInput.ExpressionKind == DbExpressionKind.Skip)
{
return new ProjectLimitSkipLifter(project, limit, (DbSkipExpression)limitInput, aliasGenerator);
}
}
}
if (source.ExpressionKind == DbExpressionKind.Skip)
{
return new SkipLifter((DbSkipExpression)source, aliasGenerator);
}
if (source.ExpressionKind == DbExpressionKind.Limit)
{
var limit = (DbLimitExpression)source;
DbExpression limitInput = limit.Argument;
if (limitInput.ExpressionKind == DbExpressionKind.Sort)
{
return new LimitSortLifter(limit, (DbSortExpression)limitInput, aliasGenerator);
}
if (limitInput.ExpressionKind == DbExpressionKind.Skip)
{
return new LimitSkipLifter(limit, (DbSkipExpression)limitInput, aliasGenerator);
}
if (limitInput.ExpressionKind == DbExpressionKind.Project)
{
var project = (DbProjectExpression)limitInput;
DbExpression projectInput = project.Input.Expression;
if (projectInput.ExpressionKind == DbExpressionKind.Sort)
{
// source.Sort(o).Project(p).Limit(k).* is equivalent to transformation for
// source.Sort(o).Limit(k).Project(p).*
return new ProjectLimitSortLifter(project, limit, (DbSortExpression)projectInput, aliasGenerator);
}
if (projectInput.ExpressionKind == DbExpressionKind.Skip)
{
// source.Skip(k, o).Project(p).Limit(k2).* is equivalent to transformation for
// source.Skip(k, o).Limit(k2).Project(p).*
return new ProjectLimitSkipLifter(project, limit, (DbSkipExpression)projectInput, aliasGenerator);
}
}
}
return new PassthroughOrderByLifter(source, aliasGenerator);
}
#region Builder methods
internal abstract DbExpression Project(DbProjectExpression project);
internal abstract DbExpression Filter(DbFilterExpression filter);
internal virtual DbExpression OfType(TypeUsage type)
{
// s.OfType<T> is normally translated to s.Filter(e => e is T).Project(e => e as T)
DbExpressionBinding rootBinding = _root.BindAs(_aliasGenerator.Next());
DbExpression filter = this.Filter(rootBinding.Filter(rootBinding.Variable.IsOf(type)));
OrderByLifterBase filterLifter = GetLifter(filter, _aliasGenerator);
DbExpressionBinding filterBinding = filter.BindAs(_aliasGenerator.Next());
DbExpression project = filterLifter.Project(filterBinding.Project(filterBinding.Variable.TreatAs(type)));
return project;
}
internal abstract DbExpression Limit(DbExpression k);
internal abstract DbExpression Skip(DbExpression k);
#endregion
#region Lambda composition: merge arguments to operators to create a single operator
protected DbProjectExpression ComposeProject(DbExpression input, DbProjectExpression first, DbProjectExpression second)
{
// source.Project(first).Project(second) -> source.Project(e => second(first(e)))
// create lambda expression representing the second projection (e => second(e))
DbLambda secondLambda = DbExpressionBuilder.Lambda(second.Projection, second.Input.Variable);
// invoke lambda with variable from the first projection
DbProjectExpression composed = first.Input.Project(secondLambda.Invoke(first.Projection));
return RebindProject(input, composed);
}
protected DbFilterExpression ComposeFilter(DbExpression input, DbProjectExpression first, DbFilterExpression second)
{
// source.Project(first).Filter(second) -> source.Filter(e => second(first(e)))
// create lambda expression representing the filter (e => second(e))
DbLambda secondLambda = DbExpressionBuilder.Lambda(second.Predicate, second.Input.Variable);
// invoke lambda with variable from the project
DbFilterExpression composed = first.Input.Filter(secondLambda.Invoke(first.Projection));
return RebindFilter(input, composed);
}
#endregion
#region Paging op reducers
protected DbSkipExpression AddToSkip(DbExpression input, DbSkipExpression skip, DbExpression plusK)
{
// source.Skip(k, o).Skip(k2) -> source.Skip(k + k2, o)
DbExpression newCount = CombineIntegers(skip.Count, plusK,
(l, r) => l + r);
return RebindSkip(input, skip, newCount);
}
protected DbLimitExpression SubtractFromLimit(DbExpression input, DbLimitExpression limit, DbExpression minusK)
{
DbExpression newCount = CombineIntegers(limit.Limit, minusK,
(l, r) => r > l ? 0 : l - r); // can't limit to less than zero rows)
return DbExpressionBuilder.Limit(input, newCount);
}
protected DbLimitExpression MinimumLimit(DbExpression input, DbLimitExpression limit, DbExpression k)
{
// source.Limit(k).Limit(k2) -> source.Limit(Min(k, k2))
DbExpression newCount = CombineIntegers(limit.Limit, k, Math.Min);
return DbExpressionBuilder.Limit(input, newCount);
}
protected DbExpression CombineIntegers(DbExpression left, DbExpression right,
Func<int, int, int> combineConstants)
{
if (left.ExpressionKind == DbExpressionKind.Constant &&
right.ExpressionKind == DbExpressionKind.Constant)
{
object leftValue = ((DbConstantExpression)left).Value;
object rightValue = ((DbConstantExpression)right).Value;
if (leftValue is int && rightValue is int)
{
return left.ResultType.Constant(combineConstants((int)leftValue, (int)rightValue));
}
}
Debug.Fail("only valid for integer constants");
throw EntityUtil.InternalError(EntityUtil.InternalErrorCode.UnexpectedLinqLambdaExpressionFormat);
}
#endregion
#region Rebinders: take an operator and apply it to a different input
protected DbProjectExpression RebindProject(DbExpression input, DbProjectExpression project)
{
DbExpressionBinding inputBinding = input.BindAs(project.Input.VariableName);
return inputBinding.Project(project.Projection);
}
protected DbFilterExpression RebindFilter(DbExpression input, DbFilterExpression filter)
{
DbExpressionBinding inputBinding = input.BindAs(filter.Input.VariableName);
return inputBinding.Filter(filter.Predicate);
}
protected DbSortExpression RebindSort(DbExpression input, DbSortExpression sort)
{
DbExpressionBinding inputBinding = input.BindAs(sort.Input.VariableName);
return inputBinding.Sort(sort.SortOrder);
}
protected DbSortExpression ApplySkipOrderToSort(DbExpression input, DbSkipExpression sortSpec)
{
DbExpressionBinding inputBinding = input.BindAs(sortSpec.Input.VariableName);
return inputBinding.Sort(sortSpec.SortOrder);
}
protected DbSkipExpression ApplySortOrderToSkip(DbExpression input, DbSortExpression sort, DbExpression k)
{
DbExpressionBinding inputBinding = input.BindAs(sort.Input.VariableName);
return inputBinding.Skip(sort.SortOrder, k);
}
protected DbSkipExpression RebindSkip(DbExpression input, DbSkipExpression skip, DbExpression k)
{
DbExpressionBinding inputBinding = input.BindAs(skip.Input.VariableName);
return inputBinding.Skip(skip.SortOrder, k);
}
#endregion
}
/// <summary>
/// Represents an expression of the form: source.Skip(k, o).Limit(k2)
/// </summary>
private class LimitSkipLifter : OrderByLifterBase
{
private readonly DbLimitExpression _limit;
private readonly DbSkipExpression _skip;
private readonly DbExpression _source;
internal LimitSkipLifter(DbLimitExpression limit, DbSkipExpression skip, AliasGenerator aliasGenerator)
: base(limit, aliasGenerator)
{
_limit = limit;
_skip = skip;
_source = skip.Input.Expression;
}
internal override DbExpression Filter(DbFilterExpression filter)
{
// source.Skip(k, o).Limit(k2).Filter(f) ->
// source.Skip(k, o).Limit(k2).Filter(f).Sort(o)
return ApplySkipOrderToSort(filter, _skip);
}
internal override DbExpression Project(DbProjectExpression project)
{
// the result is already ordered (no compensation is required)
return project;
}
internal override DbExpression Limit(DbExpression k)
{
// source.Skip(k, o).Limit(k2).Limit(k3) ->
// source.Skip(k, o).Limit(Min(k2, k3)) where k2 and k3 are constants
// otherwise source.Skip(k, o).Limit(k2).Sort(o).Limit(k3)
if (_limit.Limit.ExpressionKind == DbExpressionKind.Constant &&
k.ExpressionKind == DbExpressionKind.Constant)
{
return MinimumLimit(_skip, _limit, k);
}
else
{
return ApplySkipOrderToSort(_limit, _skip).Limit(k);
}
}
internal override DbExpression Skip(DbExpression k)
{
// source.Skip(k, o).Limit(k2).Skip(k3) ->
// source.Skip(k, o).Limit(k2).Skip(k3, o)
return RebindSkip(_limit, _skip, k);
}
}
/// <summary>
/// Represents an expression of the form: source.Sort(o).Limit(k)
/// </summary>
private class LimitSortLifter : OrderByLifterBase
{
private readonly DbLimitExpression _limit;
private readonly DbSortExpression _sort;
private readonly DbExpression _source;
internal LimitSortLifter(DbLimitExpression limit, DbSortExpression sort, AliasGenerator aliasGenerator)
: base(limit, aliasGenerator)
{
_limit = limit;
_sort = sort;
_source = sort.Input.Expression;
}
internal override DbExpression Filter(DbFilterExpression filter)
{
// source.Sort(o).Limit(k).Filter(f) -> source.Sort(o).Limit(k).Filter(f).Sort(o)
return RebindSort(filter, _sort);
}
internal override DbExpression Project(DbProjectExpression project)
{
// the result is already ordered (no compensation is required)
return project;
}
internal override DbExpression Limit(DbExpression k)
{
// source.Sort(o).Limit(k).Limit(k2) -> source.Sort(o).Limit(Min(k, k2)) when k and k2 are constants
// otherwise -> source.Sort(o).Limit(k).Sort(o).Limit(k2)
if (_limit.Limit.ExpressionKind == DbExpressionKind.Constant &&
k.ExpressionKind == DbExpressionKind.Constant)
{
return MinimumLimit(_sort, _limit, k);
}
else
{
return RebindSort(_limit, _sort).Limit(k);
}
}
internal override DbExpression Skip(DbExpression k)
{
// source.Sort(o).Limit(k).Skip(k2) -> source.Sort(o).Limit(k).Skip(k2, o)
return ApplySortOrderToSkip(_limit, _sort, k);
}
}
/// <summary>
/// Represents an expression of the form: source.Skip(k, o).Limit(k2).Project(p)
/// </summary>
/// <remarks>
/// This class is also used to represent expressions of the form: source.Skip(k, o).Project(p).Limit(k).
/// As a result, the rewrites must be spelled out entirely (the implementation cannot assume that
/// _limit exists in a particular position in the tree)
/// </remarks>
private class ProjectLimitSkipLifter : OrderByLifterBase
{
private readonly DbProjectExpression _project;
private readonly DbLimitExpression _limit;
private readonly DbSkipExpression _skip;
private readonly DbExpression _source;
internal ProjectLimitSkipLifter(DbProjectExpression project, DbLimitExpression limit, DbSkipExpression skip, AliasGenerator aliasGenerator)
: base(project, aliasGenerator)
{
_project = project;
_limit = limit;
_skip = skip;
_source = skip.Input.Expression;
}
internal override DbExpression Filter(DbFilterExpression filter)
{
// source.Skip(k, o).Limit(k2).Project(p).Filter(f) ->
// source.Skip(k, o).Limit(k2).Filter(e => f(p(e))).Sort(o).Project(p)
return RebindProject(
ApplySkipOrderToSort(
ComposeFilter(
DbExpressionBuilder.Limit(_skip, _limit.Limit),
_project,
filter),
_skip),
_project);
}
internal override DbExpression Project(DbProjectExpression project)
{
// source.Skip(k, o).Limit(k2).Project(p).Project(p2) ->
// source.Skip(k, o).Limit(k2).Project(e => p2(p(e)))
return ComposeProject(
DbExpressionBuilder.Limit(_skip, _limit.Limit),
_project,
project);
}
internal override DbExpression Limit(DbExpression k)
{
// source.Skip(k, o).Limit(k2).Project(p).Limit(k3) ->
// source.Skip(k, o).Limit(Min(k2, k3)).Project(p) where k2 and k2 are constants
// otherwise -> source.Skip(k, o).Limit(k2).Sort(o).Limit(k3).Project(p)
if (_limit.Limit.ExpressionKind == DbExpressionKind.Constant &&
k.ExpressionKind == DbExpressionKind.Constant)
{
return RebindProject(
MinimumLimit(_skip, _limit, k),
_project);
}
else
{
return RebindProject(
DbExpressionBuilder.Limit(
ApplySkipOrderToSort(
DbExpressionBuilder.Limit(_skip, _limit.Limit),
_skip),
k),
_project);
}
}
internal override DbExpression Skip(DbExpression k)
{
// source.Skip(k, o).Limit(k2).Project(p).Skip(k3) ->
// source.Skip(k + k3, o).Limit(k2 – k3).Project(p) when k, k2 and k3 are constants
// otherwise -> source.Skip(k, o).Limit(k2).Skip(k3, o).Project(p)
if (_skip.Count.ExpressionKind == DbExpressionKind.Constant &&
_limit.Limit.ExpressionKind == DbExpressionKind.Constant &&
k.ExpressionKind == DbExpressionKind.Constant)
{
return RebindProject(
SubtractFromLimit(
AddToSkip(_source, _skip, k),
_limit,
k),
_project);
}
else
{
return RebindProject(
RebindSkip(
DbExpressionBuilder.Limit(_skip, _limit.Limit),
_skip,
k),
_project);
}
}
}
/// <summary>
/// Represents an expression of the form: source.Sort(o).Limit(k).Project(p)
/// </summary>
/// <remarks>
/// This class is also used to represent expressions of the form: source.Sort(o).Project(p).Limit(k).
/// As a result, the rewrites must be spelled out entirely (the implementation cannot assume that
/// _limit exists in a particular position in the tree)
/// </remarks>
private class ProjectLimitSortLifter : OrderByLifterBase
{
private readonly DbProjectExpression _project;
private readonly DbLimitExpression _limit;
private readonly DbSortExpression _sort;
private readonly DbExpression _source;
internal ProjectLimitSortLifter(DbProjectExpression project, DbLimitExpression limit, DbSortExpression sort, AliasGenerator aliasGenerator)
: base(project, aliasGenerator)
{
_project = project;
_limit = limit;
_sort = sort;
_source = sort.Input.Expression;
}
internal override DbExpression Filter(DbFilterExpression filter)
{
// source.Sort(o).Limit(k).Project(p).Filter(f) -> source.Sort(o).Limit(k).Filter(e => f(p(e))).Sort(o).Project(p)
return RebindProject(
RebindSort(
ComposeFilter(
DbExpressionBuilder.Limit(_sort, _limit.Limit),
_project,
filter),
_sort),
_project);
}
internal override DbExpression Project(DbProjectExpression project)
{
// source.Sort(o).Limit(k).Project(p).Project(p2) -> source.Sort(o).Limit(k).Project(e => p2(p(e)))
return ComposeProject(
DbExpressionBuilder.Limit(_sort, _limit.Limit),
_project,
project);
}
internal override DbExpression Limit(DbExpression k)
{
// source.Sort(o).Limit(k).Project(p).Limit(k2) -> source.Sort(o).Limit(Min(k, k2)).Project(p) where k and k2 are constants
// otherwise -> source.Sort(o).Limit(k).Sort(o).Limit(k2).Project(p)
if (_limit.Limit.ExpressionKind == DbExpressionKind.Constant &&
k.ExpressionKind == DbExpressionKind.Constant)
{
return RebindProject(
MinimumLimit(_sort, _limit, k),
_project);
}
else
{
return RebindProject(
DbExpressionBuilder.Limit(
RebindSort(
DbExpressionBuilder.Limit(_sort, _limit.Limit),
_sort),
k),
_project);
}
}
internal override DbExpression Skip(DbExpression k)
{
// source.Sort(o).Limit(k).Project(p).Skip(k2) -> source.Sort(o).Limit(k).Skip(k2, o).Project(p)
return RebindProject(
ApplySortOrderToSkip(
DbExpressionBuilder.Limit(_sort, _limit.Limit),
_sort,
k),
_project);
}
}
/// <summary>
/// Represents an expression of the form: source.Skip(k, o).Project(p)
/// </summary>
private class ProjectSkipLifter : OrderByLifterBase
{
private readonly DbProjectExpression _project;
private readonly DbSkipExpression _skip;
private readonly DbExpression _source;
internal ProjectSkipLifter(DbProjectExpression project, DbSkipExpression skip, AliasGenerator aliasGenerator)
: base(project, aliasGenerator)
{
_project = project;
_skip = skip;
_source = _skip.Input.Expression;
}
internal override DbExpression Filter(DbFilterExpression filter)
{
// source.Skip(k, o).Project(p).Filter(f) -> source.Skip(k, o).Filter(e => f(p(e))).Sort(o).Project(p)
return RebindProject(
ApplySkipOrderToSort(
ComposeFilter(_skip, _project, filter),
_skip),
_project);
}
internal override DbExpression Limit(DbExpression k)
{
// the result is already ordered (no compensation is required)
return DbExpressionBuilder.Limit(_root, k);
}
internal override DbExpression Project(DbProjectExpression project)
{
// source.Skip(k, o).Project(p).Project(p2) -> source.Skip(k, o).Project(e => p2(p(e)))
return ComposeProject(_skip, _project, project);
}
internal override DbExpression Skip(DbExpression k)
{
// source.Skip(k, o).Project(p).Skip(k2) -> source.Skip(k + k2, o).Project(p) where k and k2 are constants,
// otherwise -> source.Skip(k, o).Skip(k2, o).Project(p)
if (_skip.Count.ExpressionKind == DbExpressionKind.Constant &&
k.ExpressionKind == DbExpressionKind.Constant)
{
return RebindProject(AddToSkip(_source, _skip, k), _project);
}
else
{
return RebindProject(RebindSkip(_skip, _skip, k), _project);
}
}
}
/// <summary>
/// Represents an expression of the form: source.Skip(k, o)
/// </summary>
private class SkipLifter : OrderByLifterBase
{
private readonly DbSkipExpression _skip;
private readonly DbExpression _source;
internal SkipLifter(DbSkipExpression skip, AliasGenerator aliasGenerator)
: base(skip, aliasGenerator)
{
_skip = skip;
_source = skip.Input.Expression;
}
internal override DbExpression Filter(DbFilterExpression filter)
{
// source.Skip(k, o).Filter(f) -> source.Skip(k, o).Filter(f).Sort(o)
return ApplySkipOrderToSort(filter, _skip);
}
internal override DbExpression Project(DbProjectExpression project)
{
// the result is already ordered (no compensation is required)
return project;
}
internal override DbExpression Limit(DbExpression k)
{
// the result is already ordered (no compensation is required)
return DbExpressionBuilder.Limit(_root, k);
}
internal override DbExpression Skip(DbExpression k)
{
// source.Skip(k, o).Skip(k2) -> source.Skip(k + k2, o) where k and k2 are both constants
// otherwise, -> source.Skip(k, o).Skip(k2, o)
if (_skip.Count.ExpressionKind == DbExpressionKind.Constant &&
k.ExpressionKind == DbExpressionKind.Constant)
{
return AddToSkip(_source, _skip, k);
}
else
{
return RebindSkip(_skip, _skip, k);
}
}
}
/// <summary>
/// Represents an expression of the form: source.Sort(o).Project(p)
/// </summary>
private class ProjectSortLifter : OrderByLifterBase
{
private readonly DbProjectExpression _project;
private readonly DbSortExpression _sort;
private readonly DbExpression _source;
internal ProjectSortLifter(DbProjectExpression project, DbSortExpression sort, AliasGenerator aliasGenerator)
: base(project, aliasGenerator)
{
_project = project;
_sort = sort;
_source = sort.Input.Expression;
}
internal override DbExpression Project(DbProjectExpression project)
{
// source.Sort(o).Project(p).Project(p2) -> source.Sort(o).Project(e => p2(p(2)))
return ComposeProject(_sort, _project, project);
}
internal override DbExpression Filter(DbFilterExpression filter)
{
// source.Sort(o).Project(p).Filter(f) -> source.Filter(e => f(p(e))).Sort(o).Project(p)
return RebindProject(
RebindSort(
ComposeFilter(_source, _project, filter),
_sort),
_project);
}
internal override DbExpression Limit(DbExpression k)
{
// the result is already ordered (no compensation is required)
return DbExpressionBuilder.Limit(_root, k);
}
internal override DbExpression Skip(DbExpression k)
{
// source.Sort(o).Project(p).Skip(k) -> source.Skip(k, o).Project(p)
return RebindProject(ApplySortOrderToSkip(_source, _sort, k), _project);
}
}
/// <summary>
/// Represents an expression for which there is an explicit order by: source.Sort(o)
/// </summary>
private class SortLifter : OrderByLifterBase
{
private readonly DbSortExpression _sort;
private readonly DbExpression _source;
internal SortLifter(DbSortExpression sort, AliasGenerator aliasGenerator)
: base(sort, aliasGenerator)
{
_sort = sort;
_source = sort.Input.Expression;
}
internal override DbExpression Project(DbProjectExpression project)
{
// the result is already ordered (no compensation is required)
return project;
}
internal override DbExpression Filter(DbFilterExpression filter)
{
// source.Sort(o).Filter(f) -> source.Filter(f).Sort(o)
return RebindSort(RebindFilter(_source, filter), _sort);
}
internal override DbExpression Limit(DbExpression k)
{
// the result is already ordered (no compensation is required)
return DbExpressionBuilder.Limit(_root, k);
}
internal override DbExpression Skip(DbExpression k)
{
// source.Sort(o).Skip(k) -> source.Skip(k, o)
return ApplySortOrderToSkip(_source, _sort, k);
}
}
/// <summary>
/// Used for sources that do not have any intrinsic order.
/// </summary>
private class PassthroughOrderByLifter : OrderByLifterBase
{
internal PassthroughOrderByLifter(DbExpression source, AliasGenerator aliasGenerator)
: base(source, aliasGenerator)
{
}
internal override DbExpression Project(DbProjectExpression project)
{
return project;
}
internal override DbExpression Filter(DbFilterExpression filter)
{
return filter;
}
internal override DbExpression OfType(TypeUsage type)
{
return DbExpressionBuilder.OfType(_root, type);
}
internal override DbExpression Limit(DbExpression k)
{
return DbExpressionBuilder.Limit(_root, k);
}
internal override DbExpression Skip(DbExpression k)
{
// since the source has no intrinsic order, we need to throw (skip
// requires order)
throw EntityUtil.NotSupported(System.Data.Entity.Strings.ELinq_SkipWithoutOrder);
}
}
}
}
}
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