QueryR

QueryR provides a simple interface for executing ad hoc queries against IQueryable<T> implementations.

This is useful in situations where there is a need to provide end users with the ability to create custom queries without increasing the complexity of the solution.

In practice you will have your own domain query criteria object that collects what you want to query. You will perform a map to the QueryR.Query object and send it to the IQueryable<T>.Query method.

If you intend to use QueryR with EntityFrameworkCore, please use QueryR.EntityFrameworkCore.

Basic Functionality Example

var kerbals = new List<Kerbal>
{
    new Kerbal { FirstName = "Bob", LastName = "Kerman" },
    new Kerbal { FirstName = "Bill", LastName = "Kerman" },
    new Kerbal { FirstName = "Jeb", LastName = "Kerman" },
    new Kerbal { FirstName = "Val", LastName = "Kerman" },
};

//Note: 
var queryResult = kerbals.AsQueryable().Query(new Filter
{
    PropertyName = nameof(Kerbal.FirstName),
    Operator = FilterOperators.StartsWith,
    Value = "B"
}).ToList();

Console.WriteLine($"Filter matched {queryResult.Count} Kerbal(s). They are:");
foreach(var item in queryResult)
{
    Console.WriteLine($" - {item.FirstName}");
}

// Expected Output :
// Filter matched 2 Kerbal(s). They are:
//  - Bob
//  - Bill

QueryR Full Functionality Example

QueryR can perform the following IQueryActions.

• Filter - Reduce the amount of records returned by specifying conditions. Does not support "OR", if you need "OR", run a seond query.
• Paging
• Sort
• Sparse Fieldsets - Restrict the fields returned for a specified entity.

var (Count, Items) = kerbals.AsQueryable().Query(new Query
{
    Filters = new List<Filter>
    {
        new Filter
        {
            PropertyName = nameof(Kerbal.FirstName),
            Operator = FilterOperators.Contains,
            Value = "l"
        },
    },
    PagingOptions = new PagingOptions
    {
        PageNumber = 2,
        PageSize = 1
    },
    Sorts = new List<Sort>
    {
        new Sort
        {
            IsAscending = false,
            PropertyName = nameof(Kerbal.FirstName)
        },
    },
    SparseFields = new List<SparseField>
    {
        new SparseField
        {
            EntityName = nameof(Kerbal),
            PropertyNames = new List<string> { nameof(Kerbal.FirstName) }
        },
    }
}).GetCountAndList();

Console.WriteLine($"{Count} Kerbal(s) match filter, {Items.Count} Kerbal(s) returned:");
foreach(var item in queryResult)
{
    Console.WriteLine($" - {item.FirstName} {item.LastName} was found.");
}

// Expected output:
// 2 Kerbal(s) match filter, 1 Kerbal(s) returned:
// - Bill  was found.

QueryR Filters

QueryR provides the following filters:

• Equal
• GreaterThan
• GreaterThanOrEqual
• LessThan
• LessThanOrEqual
• NotEqual
• Contains
• In
• StartsWith
• EndsWith
• CollectionContains

Extra filters can be defined and used as if they were a part of QueryR. For example, if a string length filter was needed.

We could do

public static class ExtendedFilterOperators
{
    public static readonly FilterOperator LengthLessThan = new FilterOperator("llt", nameof(LengthLessThan),
        (property, target) => Expression.LessThan(Expression.Property(property, nameof(string.Length)), target));
}

and use it like so

var queryResult = kerbals.AsQueryable().Query(new Filter
{
    PropertyName = nameof(Kerbal.FirstName),
    Operator = ExtendedFilterOperators.LengthLessThan,
    Value = 4
}).ToList();

Console.WriteLine($"Filter matched {queryResult.Count} Kerbal(s). They are:");
foreach(var item in queryResult)
{
    Console.WriteLine($" - {item.FirstName}");
}

// Expected Output :
// Filter matched 3 Kerbal(s). They are:
//  - Bob
//  - Jeb
//  - Val

Working Example

For a working example of QueryR in action, check out the ConsoleApp example.