Pozitron.QuerySpecification.EntityFrameworkCore 11.0.0-beta1

A .NET library for building query specifications.

• Pozitron.QuerySpecification A base package containing the core functionality, in-memory evaluators, and validators.
• Pozitron.QuerySpecification.EntityFrameworkCore An EntityFramework Core plugin to the base package. It contains EF specific evaluators.

Getting Started

An extended list of features (in-memory collection evaluations, validations, repositories, extensions, etc.) will be soon available in the Wiki. Below are listed some basic and common usages.

Creating and consuming specifications

Create your specifications by inheriting from the Specification<T> class, and use the Query builder in the constructor to define your conditions.

public class CustomerSpec : Specification<Customer>
{
  public CustomerSpec(int age, string nameTerm)
  {
    Query
      .Where(x => x.Age >= age)
      .Like(x => x.Name, $"%{nameTerm}%")
      .Include(x => x.Addresses)
          .ThenInclude(x => x.Contact)
      .OrderBy(x => x.Id)
          .ThenBy(x => x.Name)
      .Skip(10)
      .Take(10)
      .AsSplitQuery();
  }
}

Apply the specification to DbSet<T> or IQueryable<T> source.

var spec = new CustomerSpec(30, "Customer");

List<Customer> result = await _context
    .Customers
    .WithSpecification(spec)
    .ToListAsync();

Projections

The specification can be used to project the result into a different type. Inherit from Specification<T, TResult> class, where TResult is the type you want to project into. This offers strongly typed experience in the builder and during the evaluation.

public class CustomerDtoSpec : Specification<Customer, CustomerDto>
{
  public CustomerDtoSpec(int age, string nameTerm)
  {
    Query
      .Where(x => x.Age >= age)
      .Like(x => x.Name, $"%{nameTerm}%")
      .OrderBy(x => x.Name)
      .Select(x => new CustomerDto(x.Id, x.Name));
  }
}

Apply the specification to DbSet<T> or IQueryable<T> source.

var spec = new CustomerDtoSpec(30, "Customer");

List<CustomerDto> result = await _context
    .Customers
    .WithSpecification(spec)
    .ToListAsync();

Pagination

The library defines a convenient ToPagedResult extension method that returns a detailed paginated result.

var spec = new CustomerDtoSpec(1, "Customer");
var pagingFilter = new PagingFilter
{
    Page = 1,
    PageSize = 2
};

PagedResult<CustomerDto> result = await _context
    .Customers
    .WithSpecification(spec)
    .ToPagedResultAsync(pagingFilter);

The PagedResult<T> is serializable and contains a detailed pagination information and the data.

{
  "Pagination": {
    "TotalItems": 100,
    "TotalPages": 50,
    "PageSize": 2,
    "Page": 1,
    "StartItem": 1,
    "EndItem": 2,
    "HasPrevious": false,
    "HasNext": true
  },
  "Data": [
    {
      "Id": 1,
      "Name": "Customer 1"
    },
    {
      "Id": 2,
      "Name": "Customer 2"
    }
  ]
}

Benchmarks

In version 11, we refactored and rebuilt the internals from the ground up. The new version reduces the memory footprint drastically. The overhead of the library is now negligible and statistically insignificant. Here are the benchmark results of ToQueryString() for various queries. Refer to the Benchmarks project for more benchmarks.

Type:

• 0 → Empty
• 1 → Single Where clause
• 2 → Where and OrderBy
• 3 → Where, Order chain, Include chain, Flag (AsNoTracking)
• 4 → Where, Order chain, Include chain, Like, Skip, Take, Flag (AsNoTracking)

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