public static Expression Extract <T>(IQueryable qry, ParameterExpression parameterExpression, string parameterName)
{
MethodCallExpression methodCallExpression = qry.Expression as MethodCallExpression;
Expression <Func <LambdaExpression> > executionLambda = Expression.Lambda <Func <LambdaExpression> >(methodCallExpression.Arguments[1]);
Expression extractedExpression = (executionLambda.Compile().Invoke() as Expression <Func <T, bool> >).Body;
var filterExpressionVisitor = new ParameterExpressionVisitor(parameterExpression, parameterName);
return(filterExpressionVisitor.Visit(extractedExpression));
}
/// <summary>
/// Extracts the "Where" clause Expression from an IQueryable
/// </summary>
/// <param name="qry">The qry.</param>
/// <param name="parameterExpression">The original parameter expression.</param>
/// <param name="parameterName">Name of the parameter (forexample: 'p') from the qry to replace with the parameterExpression.</param>
/// <returns></returns>
public static Expression Extract(IQueryable qry, ParameterExpression parameterExpression, string parameterName)
{
var methodCallExpression = qry.Expression as MethodCallExpression;
if (methodCallExpression == null)
{
return(null);
}
var executionLambda = Expression.Lambda <Func <LambdaExpression> >(methodCallExpression.Arguments[1]);
var extractedExpression = (executionLambda.Compile().Invoke()).Body;
var filterExpressionVisitor = new ParameterExpressionVisitor(parameterExpression, parameterName);
return(filterExpressionVisitor.Visit(extractedExpression));
}
/// <summary>
/// Replaces a parameter in the expression.
/// </summary>
/// <param name="expression">The expression.</param>
/// <param name="parameterName">Name of the parameter to be replaced.</param>
/// <param name="parameterExpression">The parameter expression to use in the replacement.</param>
/// <returns>A new Expression if the original expression was modified; otherwise the original expression.</returns>
public static Expression ReplaceParameter(this Expression expression, string parameterName, ParameterExpression parameterExpression)
{
var filterExpressionVisitor = new ParameterExpressionVisitor(parameterExpression, parameterName);
return(filterExpressionVisitor.Visit(expression));
}