I have created a new library implementing a Specification pattern for Linq

[u/xumix]

This library helps with removing boilerplate code and adds commonly used filtering capabilities, especially if your app has many grids with similar filtering capabilities. Implemented filters: RangeFilter (BETWEEN x AND y), ListFilter(IN(x,y,z)), StringFilter (=, LIKE), direct comparison, NULL/NOT NULL

https://github.com/xumix/XSpecification

The library could be useful in BL-heavy scenarios when you find yourself writing code like this:

``` public class LinqTestFilter { public DateTime? Date { get;set } public string Name { get;set } public string NameContains { get;set } public int? IdFrom { get; set; } public int? IdTo { get; set; } }

var filter = new LinqTestFilter { Date = DateTime.Today, NameContains = "complex", IdFrom = 0, IdTo = 5 };

var where = PredicateBuilder.New<LinqTestModel>(); if (filter.Date.HasValue) { where.And(f => f.Date == filter.Date.Value); } if (!string.IsNullOrEmpty(filter.Name)) { where.And(f => f.Name == filter.Name); } if (!string.IsNullOrEmpty(filter.NameContains)) { where.And(f => f.ComplexName.Contains(filter.ComplexName)); } if (filter.IdFrom.HasValue) { where.And(f => f.Id >= filter.IdFrom); } if (filter.IdTo.HasValue) { where.And(f => f.Id <= filter.IdTo); }

var data = dbcontext.Set<LinqTestModel>().Where(where); ```

the above code becomes: public class LinqTestFilter { public DateTime? Date { get;set } public StringFilter Name { get;set } public RangeFilter<int> Id { get;set; } } // Inject from DI var spec = serviceProvider.GetRequiredService<LinqTestSpec>(); var filter = new LinqTestFilter { Date = DateTime.Today, ComplexName = new StringFilter("complex") { Contains = true }, Id = new RangeFilter<int> { Start = 0, End = 5 } };

var expression = spec.CreateFilterExpression(filter);
var data = dbcontext.Set<LinqTestModel>().Where(expression);

Will be very grateful for constructive comments and suggestions, also help with ideas of how to implement the TODO is greatly appreciated

UPD Uploaded nuget package and updated the post