// Executes the expression tree that is passed to it.
internal static object Execute(Expression expression, bool IsEnumerable)
{
// The expression must represent a query over the data source.
if (!IsQueryOverDataSource(expression))
{
throw new InvalidProgramException("No query over the data source was specified.");
}
// Find the call to Where() and get the lambda expression predicate.
InnermostWhereFinder whereFinder = new InnermostWhereFinder();
MethodCallExpression whereExpression = whereFinder.GetInnermostWhere(expression);
LambdaExpression lambdaExpression = (LambdaExpression)((UnaryExpression)(whereExpression.Arguments[1])).Operand;
// Send the lambda expression through the partial evaluator.
lambdaExpression = (LambdaExpression)Evaluator.PartialEval(lambdaExpression);
// Get the place name(s) to query the Web service with.
LocationFinder lf = new LocationFinder(lambdaExpression.Body);
List <string> locations = lf.Locations;
if (locations.Count == 0)
{
throw new InvalidQueryException("You must specify at least one place name in your query.");
}
// Call the Web service and get the results.
Place[] places = WebServiceHelper.GetPlacesFromTerraServer(locations);
// Copy the IEnumerable places to an IQueryable.
IQueryable <Place> queryablePlaces = places.AsQueryable <Place>();
// Copy the expression tree that was passed in, changing only the first
// argument of the innermost MethodCallExpression.
ExpressionTreeModifier treeCopier = new ExpressionTreeModifier(queryablePlaces);
Expression newExpressionTree = treeCopier.CopyAndModify(expression);
// This step creates an IQueryable that executes by replacing Queryable methods with Enumerable methods.
if (IsEnumerable)
{
return(queryablePlaces.Provider.CreateQuery(newExpressionTree));
}
else
{
return(queryablePlaces.Provider.Execute(newExpressionTree));
}
}
// 执行传递给它的表达式树。
internal static object Execute(Expression expression, bool IsEnumerable)
{
// 表达式必须代表对数据源的查询。
if (!IsQueryOverDataSource(expression))
{
throw new InvalidProgramException("No query over the data source was specified.");
}
// 找到对 Where() 的调用，并获取 lambda 表达式谓词。
InnermostWhereFinder whereFinder = new InnermostWhereFinder();
MethodCallExpression whereExpression = whereFinder.GetInnermostWhere(expression);
LambdaExpression lambdaExpression = (LambdaExpression)((UnaryExpression)(whereExpression.Arguments[1])).Operand;
// 通过分部计算器发送 lambda 表达式。
lambdaExpression = (LambdaExpression)Evaluator.PartialEval(lambdaExpression);
// 获取要用于查询 Web 服务的位置名称。
LocationFinder lf = new LocationFinder(lambdaExpression.Body);
List <string> locations = lf.Locations;
if (locations.Count == 0)
{
throw new InvalidQueryException("You must specify at least one place name in your query.");
}
// 调用 Web 服务并获取结果。
Place[] places = WebServiceHelper.GetPlacesFromTerraServer(locations);
// 将 IEnumerable 位置复制到 IQueryable。
IQueryable <Place> queryablePlaces = places.AsQueryable <Place>();
// 复制传入的表达式，只更改
// 最内侧 MethodCallExpression 的第一个参数。
ExpressionTreeModifier treeCopier = new ExpressionTreeModifier(queryablePlaces);
Expression newExpressionTree = treeCopier.CopyAndModify(expression);
// 此步骤将创建一个 IQueryable，它通过用可枚举方法替代可查询方法方法执行。
if (IsEnumerable)
{
return(queryablePlaces.Provider.CreateQuery(newExpressionTree));
}
else
{
return(queryablePlaces.Provider.Execute(newExpressionTree));
}
}
// Выполняет дерево выражений, которое ему передается.
internal static object Execute(Expression expression, bool IsEnumerable)
{
// Выражение должно представлять запрос к источнику данных.
if (!IsQueryOverDataSource(expression))
{
throw new InvalidProgramException("No query over the data source was specified.");
}
// Найти вызов к Where() и получить предикат лямбда-выражения.
InnermostWhereFinder whereFinder = new InnermostWhereFinder();
MethodCallExpression whereExpression = whereFinder.GetInnermostWhere(expression);
LambdaExpression lambdaExpression = (LambdaExpression)((UnaryExpression)(whereExpression.Arguments[1])).Operand;
// Переслать лямбда-выражение через частичный вычислитель.
lambdaExpression = (LambdaExpression)Evaluator.PartialEval(lambdaExpression);
// Получить имя (имена) вхождений для использования в запросе к веб-службе.
LocationFinder lf = new LocationFinder(lambdaExpression.Body);
List <string> locations = lf.Locations;
if (locations.Count == 0)
{
throw new InvalidQueryException("You must specify at least one place name in your query.");
}
// Вызвать веб-службу и получить результаты.
Place[] places = WebServiceHelper.GetPlacesFromTerraServer(locations);
// Скопировать вхождения IEnumerable в IQueryable.
IQueryable <Place> queryablePlaces = places.AsQueryable <Place>();
// Скопировать переданное дерево выражений, меняя только первый
// аргумент внутреннего MethodCallExpression.
ExpressionTreeModifier treeCopier = new ExpressionTreeModifier(queryablePlaces);
Expression newExpressionTree = treeCopier.CopyAndModify(expression);
// На этом этапе создается IQueryable, который заменяет методы Queryable на методы Enumerable.
if (IsEnumerable)
{
return(queryablePlaces.Provider.CreateQuery(newExpressionTree));
}
else
{
return(queryablePlaces.Provider.Execute(newExpressionTree));
}
}