Hi I'm wondering what the best approach would be to parse an OData $filter string in C#, for example
/API/organisations?$filter="name eq 'Facebook' or name eq 'Twitter' and subscribers gt '30'"
Should return all organisations with a name of Facebook or Twitter and who have more than 30 subscribers. I've researched quite a bit but can't find any solutions which don't revolve around WCF. I was thinking of using Regex and grouping them so I have a list of Filter classes such that:
Filter
Resource: Name
Operator: Eq
Value: Facebook
Filter
Resource: Name
Operator: Eq
Value: Twitter
Filter
Resource: Subscribers
Operator: gt
Value: 30
but I'm stumped as how to handle ANDs / ORs.
In .NET, there's a library available that will do this for you. Writing your own regex runs the risk of missing some edge case.
Using NuGet, bring in Microsoft.Data.OData. Then, you can do:
using Microsoft.Data.OData.Query;
var result = ODataUriParser.ParseFilter(
"name eq 'Facebook' or name eq 'Twitter' and subscribers gt 30",
model,
type);
result
here will be in the form of an AST representing the filter clause.
(To get the model
and type
inputs, you could parse your $metadata file using something like this:
using Microsoft.Data.Edm;
using Microsoft.Data.Edm.Csdl;
IEdmModel model = EdmxReader.Parse(new XmlTextReader(/*stream of your $metadata file*/));
IEdmEntityType type = model.FindType("organisation");
)