/// <summary>
/// Replaces the given expression.
/// </summary>
/// <param name="expression">Expression to replace.</param>
/// <returns>Replaced expression.</returns>
public virtual QueryExpression Visit(QueryAsExpression expression)
{
var source = this.ReplaceExpression(expression.Source);
if (this.HasChanged(expression.Source, source))
{
return(CommonQueryBuilder.As(source, expression.TypeToOperateAgainst));
}
return(expression);
}
/// <summary>
/// Resolves types for the specified expression.
/// </summary>
/// <param name="expression">The expression to resolve types for.</param>
/// <returns>Expression with resolved types.</returns>
public QueryExpression Visit(QueryConstantExpression expression)
{
if (expression.ExpressionType.IsUnresolved)
{
var value = expression.ScalarValue.Value;
ExceptionUtilities.Assert(value != null, "Constant expression with unresolved type cannot have null value.");
var queryType = this.GetQueryScalarTypeFromObjectValue(value);
return(CommonQueryBuilder.Constant(queryType.CreateValue(value)));
}
return(expression);
}
/// <summary>
/// Evaluates the specified expression.
/// </summary>
/// <param name="expression">The expression to evaluate.</param>
/// <returns>Value of the expression.</returns>
public virtual QueryValue Visit(QueryCustomFunctionCallExpression expression)
{
QueryValue result;
var argumentValues = this.EvaluateArguments(expression.Arguments);
var customEvaluator = expression.Function.Annotations.OfType <FunctionEvaluatorAnnotation>().Select(a => a.FunctionEvaluator).SingleOrDefault();
if (customEvaluator != null)
{
result = customEvaluator(expression.ExpressionType, argumentValues);
}
else if (expression.FunctionBody != null)
{
QueryExpression functionBody = expression.FunctionBody;
// replace parameter refs with arguments
if (expression.Function.Parameters.Any())
{
// Consider query:
// "select value DefaultNamespace.GetCustomer(c.CustomerId) from [DefaultContainer].[Customer] as c" where GetCustomer is a function.
// After we replace parameter references in the function's body with "c.CustomerId" expression evaluation
// of the body expression fails becuase variable "c" is not in the scope for the function's body.
// Note also that function body itself can have a variable reference with the same name "c".
// So the right thing is to evaluate each argument and then replace parameter references with constant expressions.
// However QueryConstantExpression currently only supports QueryScalarType/QueryScalarValue.
// So for now we only evaluating scalar arguments.
// TODO: add supoort for non-scalar constants and change the following code to evaluate each argument
// NOTE: we have similar limitation in LinqToEntitiesEvaluator
List <QueryExpression> evaluatedArguments = new List <QueryExpression>();
foreach (var argument in expression.Arguments)
{
QueryScalarType scalarArgumentType = argument.ExpressionType as QueryScalarType;
if (scalarArgumentType != null)
{
QueryScalarValue scalarValue = (QueryScalarValue)this.Evaluate(argument);
var constant = CommonQueryBuilder.Constant(scalarValue);
evaluatedArguments.Add(constant);
}
else
{
evaluatedArguments.Add(argument);
}
}
var visitor = this.CreateFunctionParameterReferenceReplacingVisitor(expression.Function, evaluatedArguments);
functionBody = visitor.ReplaceExpression(expression.FunctionBody);
}
result = this.Evaluate(functionBody);
}
else
{
result = expression.ExpressionType.EvaluationStrategy.EvaluateFunction(
expression.ExpressionType,
expression.Function,
argumentValues);
}
return(result);
}
