PredicateBuilder: OR condition nested inside .And()

问题

I'm using PredicateBuilder to build a query against a List of Umbraco Nodes to filter search results. I have the searched ID value coming through as a String via the QueryString which I then compare to a string field on each of the Umbraco Nodes in the list to get matches.

Currently, the code does the match against the target field in there is a value in the Query String which works fine. I need to add a conditional inside my .And() that tries to match the QS against the field String if the field has a value, but if the field has no value, then it should match that as well.

    if (!string.IsNullOrEmpty(qsId))
    {
       predicate = predicate.And(i => 
       Regex.IsMatch(i.GetProperty("makeTag").Value.ToString(), "\\b" + 
       qsId + "\\b"));
    }

I tried the following but it didn't seem to work properly:

    if (!string.IsNullOrEmpty(qsId))
    {
       predicate = predicate.And(i => 
       Regex.IsMatch(i.GetProperty("makeTag").Value.ToString(), "\\b" + 
       qsId + "\\b") || 
       string.IsNullOrEmpty(i.GetProperty("makeTag")).Value.ToString());
    }

Any ideas about what I'm doing incorrectly or perhaps a better way to approach this?

回答1:

for nesting or in and, you can:

create the or first, then and the or:

if (!string.IsNullOrEmpty(qsId))
{
    // default false
        var inner = PredicateBuilder.False<Product>();

    // first or
    inner = inner.Or (i => 
           Regex.IsMatch(i.GetProperty("makeTag").Value.ToString(), "\\b" + 
           qsId + "\\b");

    // second or       
    inner = inner.Or (i => 
        string.IsNullOrEmpty(i.GetProperty("makeTag")).Value.ToString());


    predicate = predicate.And(inner);
}

below was my original answer, did not relaize need nested or in and

original answer

If I understand you correctly, you are trying to achieve (when hard coding it):

Where(i => 
   Regex.IsMatch(i.GetProperty("makeTag").Value.ToString(), "\\b" + 
   qsId + "\\b" ||  string.IsNullOrEmpty(i.GetProperty("makeTag")).Value.ToString())

if so, then using predicate builder, it should do it like:

if (!string.IsNullOrEmpty(qsId))
{

    // default false
    var predicate = PredicateBuilder.False<Product>();

    // first or
    predicate = predicate.Or (i => 
           Regex.IsMatch(i.GetProperty("makeTag").Value.ToString(), "\\b" + 
           qsId + "\\b");

    // second or       
    predicate = predicate.Or (i => 
        string.IsNullOrEmpty(i.GetProperty("makeTag")).Value.ToString());
}

more example of prediccate builder, check out: http://www.albahari.com/nutshell/predicatebuilder.aspx

来源：https://stackoverflow.com/questions/45268997/predicatebuilder-or-condition-nested-inside-and

标签

.net

string

umbraco

predicatebuilder