OData in .NET Core

State of the Union

Rainer Stropek | software architects | @rstropek

Introduction

Agenda, Material

Rainer Stropek

MVP for Azure and Developer Technologies
Microsoft Regional Director

 

Passionate programmer, entrepreneur,
  teacher, dancer

 

rainer@software-architects.at
@rstropek
https://rainerstropek.me

 

Agenda, Material

  • Why OData?
  • OData Fundamentals
  • OData and .NET Core
    • Server
    • Client

https://aka.ms/AA6y96v
https://slides.com/rainerstropek/odata-netcore

Why?

What's the Problem?

/customers

/customers/ALFKI

List of all
customers

Details of
ALFKI

...

/customers

/customers/ALFKI

List of all
customers

Details of
ALFKI

List sorted
by country

/customersByCountry

Only new
customers

/newCustomers

/newCustomersByCountry

...

/customers

/customers/ALFKI

List of all
customers

Details of
ALFKI

List sorted
by country

/customersByCountry

Only new
customers

/newCustomers

/newCustomersByCountry

...

Sorting, filtering, etc.

/customers

/customers/ALFKI

List of all
customers

Details of
ALFKI

List sorted
by country

/customersByCountry

Only new
customers

/newCustomers

/newCustomersByCountry

...

Sorting, filtering, etc.

  • Data access protocol for the web
    • Similar to SQL
    • Works with HTTP
    • Platform-neutral
  • Standardization to enable generic clients
    • Metadata
    • Data encoding
    • Read and write data

Enter: OData

Enter: OData

  • ISO/IEC approved, OASIS standard
  • RESTful design principles
  • Platform agnostic, vendor-neutral
    • Primarily driven by Microsoft and SAP
    • Powerful protocol, therefore hard without framework
    • Server-side practically bound to .NET

OData Protocol

https://api.myserver.com/odata/$metadata

https://api.myserver.com/odata/Customers?
   $filter=CustomerID eq 15&
   $top=10&
   $select=FirstName,LastName
  • Protocol specification (docs)
  • Requesting metadata (docs)
  • Reading data (docs)
  • Writing data (docs)
  • Conformance levels (docs)

Not Just Basic Queries...

# Return all Categories containing more than two products whose price is greater than 5.00.
http://host/service/Categories?$filter=Products/$count($filter=Price gt 5.00) gt 2

# Return all Orders that have any Items with a Quantity greater than 100
http://host/service/Orders?$filter=Items/any(d:d/Quantity gt 100)

# Return customers along with their orders that shipped to the same city as the customer's address
http://host/service/Customers?$expand=Orders($filter=$it/Address/City eq ShipTo/City)
  • Not as flexible as SQL
  • Predefined navigation over navigation properties
  • Demo
    • Query open OData services using HTTP client (source)
    • XOData
    • Consume OData in Power BI (Query)
    • Access Microsoft Graph using OData
      ($select, $filter on calendar)

Let's Start Coding...

OData Server with .NET Core

OData with Entity Framework

  • EF Core is a good foundation for OData services
    • Note: Not a prerequisite!
  • OData uses IQueryable​ for queries






     
  • POST, PUT/PATCH, DELETE for writing
    • Similar to regular ASP.NET Core
    • Not covered here

URL

Parser

OData AST

IQueryable

C# Expression Tree

SQL

EF Core

OData Client

Drawbacks

  • Implementing OData service without EF is rather complicated
    • Demo
  • Not fully compatible with ASP.NET Core 3.1
    • Endpoint routing is still missing
  • Many tools are legacy and not maintained
    • E.g. client code generator, RESTier

Summary

Summary

  • OData is great if you need a CRUD service
  • OData gives client a lot of control
    • No need to do client-side filtering, sorting, etc.
  • Platform-independent and - theoretically - vendor-neutral
  • Documentation could be enhanced
  • Some pieces smell a little bit like legacy 😉
    • Basic .NET Core 3.1 support exists

Thank you for attending!