Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / DataEntity / System / Data / Common / CommandTrees / Internal / DbExpressionRules.cs / 1305376 / DbExpressionRules.cs
//---------------------------------------------------------------------- //// Copyright (c) Microsoft Corporation. All rights reserved. // // // @owner [....] // @backupOwner [....] //--------------------------------------------------------------------- using System.Data.Common.CommandTrees; using System.Collections.Generic; using System.Data.Metadata.Edm; using System.Diagnostics; using System.Data.Common.Utils; using System.Linq; using System.Globalization; using System.Data.Common.CommandTrees.ExpressionBuilder; namespace System.Data.Common.CommandTrees.Internal { ////// Enacapsulates the logic that defines an expression 'rule' which is capable of transforming a candidate internal abstract class DbExpressionRule { ////// into a result DbExpression, and indicating what action should be taken on that result expression by the rule application logic. /// /// Indicates what action the rule processor should take if the rule successfully processes an expression. /// internal enum ProcessedAction { ////// Continue to apply rules, from the rule immediately following this rule, to the result expression /// Continue = 0, ////// Going back to the first rule, apply all rules to the result expression /// Reset, ////// Stop all rule processing and return the result expression as the final result expression /// Stop } ////// Indicates whether /// Theshould be called on the specified argument expression. /// that the rule should inspect and determine if processing is possible /// internal abstract bool ShouldProcess(DbExpression expression); /// true if the rule can attempt processing of the expression via themethod; otherwise false /// Attempts to process the input /// The input expression that the rule should process /// The result expression produced by the rule if processing was successful ///to produce a . /// internal abstract bool TryProcess(DbExpression expression, out DbExpression result); /// true if the rule was able to successfully process the input expression and produce a result expression; otherwisefalse /// Indicates what action - as a internal abstract ProcessedAction OnExpressionProcessed { get; } } ///value - the rule processor should take if returns true. /// /// Abstract base class for a DbExpression visitor that can apply a collection of internal abstract class DbExpressionRuleProcessingVisitor : DefaultExpressionVisitor { protected DbExpressionRuleProcessingVisitor() { } protected abstract IEnumerables during the visitor pass, returning the final result expression. /// This class encapsulates the rule application logic that applies regardless of how the ruleset - modelled as the abstract method - is provided. /// GetRules(); private static Tuple ProcessRules(DbExpression expression, List rules) { // Considering each rule in the rule set in turn, if the rule indicates that it can process the // input expression, call TryProcess to attempt processing. If successful, take the action specified // by the rule's OnExpressionProcessed action, which may involve returning the action and the result // expression so that processing can be reset or halted. for (int idx = 0; idx < rules.Count; idx++) { DbExpressionRule currentRule = rules[idx]; if (currentRule.ShouldProcess(expression)) { DbExpression result; if (currentRule.TryProcess(expression, out result)) { if (currentRule.OnExpressionProcessed != DbExpressionRule.ProcessedAction.Continue) { return Tuple.Create(result, currentRule.OnExpressionProcessed); } else { expression = result; } } } } return Tuple.Create(expression, DbExpressionRule.ProcessedAction.Continue); } private bool _stopped; private DbExpression ApplyRules(DbExpression expression) { // Driver loop to apply rules while the status of processing is 'Reset', // or correctly set the _stopped flag if status is 'Stopped'. List currentRules = this.GetRules().ToList(); var ruleResult = ProcessRules(expression, currentRules); while (ruleResult.Item2 == DbExpressionRule.ProcessedAction.Reset) { currentRules = this.GetRules().ToList(); ruleResult = ProcessRules(ruleResult.Item1, currentRules); } if (ruleResult.Item2 == DbExpressionRule.ProcessedAction.Stop) { _stopped = true; } return ruleResult.Item1; } protected override DbExpression VisitExpression(DbExpression expression) { // Pre-process this visitor's rules DbExpression result = ApplyRules(expression); if (_stopped) { // If rule processing was stopped, the result expression must be returned immediately return result; } // Visit the expression to recursively apply rules to subexpressions result = base.VisitExpression(result); if (_stopped) { // If rule processing was stopped, the result expression must be returned immediately return result; } // Post-process the rules over the resulting expression and return the result. // This is done so that rules that did not match the original structure of the // expression have an opportunity to examine the structure of the result expression. result = ApplyRules(result); return result; } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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