Equals operator returns one or all

Question

Hello everyone, 
 I'll preface this by saying I'm new to Appian, so don't assume I've tried the obvious... 
 I am picking up the administration of another person's app and using a text field to pull back information for a read-only grid. The expression is set to look at three different search fields in the interface and retrieve information based on one or more of these fields (three AND query filters), ignoring empty filters. The text queries are fine, but the numeric one is not and is configured as follows: 
 a!queryFilter(
 field: "number",
 operator: "=",
 value: ri!rinumber
 ) 
 This filter either matches exactly and returns just one record, or returns ALL records as though no filter were applied. I've removed my other filters from the query just in case and got the same result. Any ideas what might be causing this? Is it possible (or even logical) to wrap just this one filter in an if() to return a distinct value or nothing at all?

Mike Schmitt · Answer

If your query entity is set up to "ignore empty" as you've indicated, then if you pass in nothing for ri!rinumber , it will query as if you're not filtering on that field at all. If your use case requires you to return no results when ri!rinumber is blank, you might consider setting the query to not ignore empty filters, or alternatively (my preferred workaround) is wrapping the input in a null check and passing a value you know will be invalid (i.e. -1) - this is usually done from the parent, i.e. if my query is self-contained within an expression rule and i want to query a row by ID, but i want it to return blank (instead of trying to return every row) when the ID is blank - i'll replace blank values with -1 from there.

Mike Schmitt · Answer

If the rule input is of type integer (which I'm assuming, but correct me if i'm wrong), and you attempt to pass letters into it, the mandatory automatic typecasting will try to convert the letters to integer, a process which strips any letters and returns any result -- and in your case would be returning a value of null. Mind explaining a bit more about your use case to help me understand why you're expecting to pass random letters in place of a numeric id?

Mike Schmitt · Answer

In almost all cases I recommend that query entities be encapsulated in their own Expression Rule - generally speaking you usually only need one Expression Rule for any unique data store entity you want to query, configured in such a way that a subsequent user of the rule can pass one or more parameters (mapping to filter values, etc), and that additional filtering parameters can be added in the future without negatively impacting the existing uses. In this way you could simply test the query against different inputs in a rapid-fire way and see how it reacts. I suggest you try that with your query here, since it might let you more easily discover how something is behaving differently from your expectations.