public static IQueryable <T> Search <T>(this IQueryable <T> source,
string searchTerm,
params Expression <Func <T, string> >[] stringProperties)
{
if (String.IsNullOrEmpty(searchTerm))
{
return(source);
}
var searchTermExpression = Expression.Constant(searchTerm);
//Variable to hold merged 'OR' expression
Expression orExpression = null;
//Retrieve first parameter to use accross all expressions
var singleParameter = stringProperties[0].Parameters.Single();
//Build a contains expression for each property
foreach (var stringProperty in stringProperties)
{
//Syncronise single parameter accross each property
var swappedParamExpression = SwapExpressionVisitor.Swap(stringProperty, stringProperty.Parameters.Single(), singleParameter);
//Build expression to represent x.[propertyX].Contains(searchTerm)
var containsExpression = BuildContainsExpression(swappedParamExpression, searchTermExpression);
orExpression = BuildOrExpression(orExpression, containsExpression);
}
var completeExpression = Expression.Lambda <Func <T, bool> >(orExpression, singleParameter);
return(source.Where(completeExpression));
}
private IEnumerable <Expression <Func <TSource, TResult> > > AlignParameters <TSource, TResult>(Expression <Func <TSource, TResult> >[] properties, ParameterExpression parameterExpression)
{
for (int i = 0; i < properties.Length; i++)
{
var property = properties[i];
yield return(SwapExpressionVisitor.Swap(property, property.Parameters.Single(), parameterExpression));
}
}
/// <summary>
/// Align the lambda parameter to that of the first string property
/// </summary>
protected Expression <TProperty> AlignParameter <TProperty>(Expression <TProperty> lambda)
{
return(SwapExpressionVisitor.Swap(lambda, lambda.Parameters.Single(), FirstParameter));
}