Filtering grammar ✍

The filtering grammar is designed to be SQL-like. You can reference fields or properties of objects in a C# style and use familiar dotted access.

Let’s start with an example. Considering this simple object:

public class World
{
    public IEnumerable<Country> Countries => new[]
    { 
        Country.US,
        Country.UK,
        Country.France
    };

    public RandomStatistics Statistics { get; }
        = new RandomStatistics();
}

public class RandomStatistics
{
    public long Population => 8007821437;

    public long Websites => 1630322759;

    public long FieldOfDreams = 201;
}

Given the object World the filter Statistics.FieldOfDreams == 201 would return true. So would the filter Statistics.Population > 1000000. As would the filter Statistics.FieldOfDreams == 201 AND Statistics.Population > 1000000.

Language elements 🧩

The following language elements are available:

Name	Function
Comparison	Allows values to be compared to eachother. Operators are `=`, `==`, `!=`, `<>`, `>`, `>=`, `<`, `<=`.
Binary	Allows two results to be combined using `AND` or `OR` (or `&&` or `\|\|`). More complex structures can be facilitated through the use of parentheses.
BETWEEN	Allows checking whether a value is between a lower and upper bound. Can also be stated as NOT BETWEEN.
IN	Allows checking whether a value is in a specified list of values.
NOT	Allows an expression to be negated.
Field Reference	Access to a member with dotted syntax (e.g. `Statistics.Population`).
Enumerable	Allows running a comparison against the elements in an `IEnumerable` - with HAS_ANY, HAS_SINGLE and HAS_NONE being available
IS NULL	Allows checking if a value is null. Can also be stated as IS NOT NULL.
LIKE	Allows checking if a value matches a SQL LIKE pattern. Patterns can include character ranges `[a-z]`, single character wildcards `?` and multiple character wildcards `%`. Can also be stated as NOT LIKE.

Some good examples of usage can be found in the unit tests.

Combining language elements 🚧

You can combine any of the individual language elements to create more complex filters. Here are some examples:

Statistics.FieldOfDreams == 201 AND Statistics.Population > 1000000

Statistics.FieldOfDreams == 201 OR (Statistics.Population > 1000000 AND Statistics.Websites > 5000)

Statistics.FieldOfDreams == 201 OR Statistics.Population > 1000000 OR Statistics.Websites > 5000

Field selectors 👈

Field selectors just use a comma separated list of field reference elements. The idea of this is to allow natural input to select a list of fields. An example would be Statistics.Population, Statistics.Websites. The field selectors would create a list of FieldSelector instances which contain the name of the field and a delegate to extract the value given an IFieldReferenceResolver instance.