/// <summary>
/// Constructs a <see cref="LambdaExpression"/> that is able to extract a specific simple <paramref name="searchedExpression"/> from a
/// complex <paramref name="fullExpression"/>.
/// </summary>
/// <param name="searchedExpression">The expression an accessor to which should be created.</param>
/// <param name="fullExpression">The full expression containing the <paramref name="searchedExpression"/>.</param>
/// <param name="inputParameter">The input parameter to be used by the resulting lambda. Its type must match the type of <paramref name="fullExpression"/>.</param>
/// <remarks>The <see cref="AccessorFindingExpressionTreeVisitor"/> compares the <paramref name="searchedExpression"/> via reference equality,
/// which means that exactly the same expression reference must be contained by <paramref name="fullExpression"/> for the visitor to return the
/// expected result. In addition, the visitor can only provide accessors for expressions nested in <see cref="NewExpression"/> or
/// <see cref="MemberInitExpression"/>.</remarks>
/// <returns>A <see cref="LambdaExpression"/> acting as an accessor for the <paramref name="searchedExpression"/> when an input matching
/// <paramref name="fullExpression"/> is given.
/// </returns>
public static LambdaExpression FindAccessorLambda(Expression searchedExpression, Expression fullExpression, ParameterExpression inputParameter)
{
ArgumentUtility.CheckNotNull("searchedExpression", searchedExpression);
ArgumentUtility.CheckNotNull("fullExpression", fullExpression);
ArgumentUtility.CheckNotNull("inputParameter", inputParameter);
if (inputParameter.Type != fullExpression.Type)
{
throw new ArgumentException(
string.Format("The inputParameter's type '{0}' must match the fullExpression's type '{1}'.", fullExpression.Type, inputParameter.Type),
"inputParameter");
}
var visitor = new AccessorFindingExpressionTreeVisitor(searchedExpression, inputParameter);
visitor.VisitExpression(fullExpression);
if (visitor.AccessorPath != null)
{
return(visitor.AccessorPath);
}
else
{
var message = string.Format(
"The given expression '{0}' does not contain the searched expression '{1}' in a nested NewExpression with member assignments or a "
+ "MemberBindingExpression.",
FormattingExpressionTreeVisitor.Format(fullExpression),
FormattingExpressionTreeVisitor.Format(searchedExpression));
throw new ArgumentException(message, "fullExpression");
}
}
protected override Expression VisitQuerySourceReferenceExpression(QuerySourceReferenceExpression expression)
{
ArgumentUtility.CheckNotNull("expression", expression);
try
{
var accessorLambda = AccessorFindingExpressionTreeVisitor.FindAccessorLambda(expression, _itemExpression, _lambdaParameter);
return(accessorLambda.Body);
}
catch (ArgumentException ex)
{
var message = string.Format(
"Cannot create a LambdaExpression that retrieves the value of '{0}' from items with a structure of '{1}'. The item expression does not "
+ "contain the value or it is too complex.",
FormattingExpressionTreeVisitor.Format(expression),
FormattingExpressionTreeVisitor.Format(_itemExpression));
throw new InvalidOperationException(message, ex);
}
}