Building RESTfull Data Services with WebAPI

Building RESTfull
Data Services
with WebAPI
Gert Drapers (#DataDude)
Principle Software Design Engineer

Agenda
•Overview
•OData Core Libraries
•Web API
•Web API Demo

OData Value Proposition
• Problem Statement:
• There is no consistent data interoperability protocol for addressing
and manipulating enterprise data across various devices and
platforms
• Value Proposition:
• OData enables consistent REST-based data access from a variety
of back ends including relational databases, file systems, content
management systems, and traditional Web sites
• OData builds on widely-accepted standards like HTTP, JSON,
AtomPub, and URIs to address and access data

What OData Is and Is Not?
• What OData Is:
• Easy, consistent data access via HTTP endpoints
• REST-based data operations: CRUD, Filtering, Sorting, Paging,
Custom Operations, Delta, etc.
• Service centric data definition, operation and annotation
• Schematized and schema-less data sets
• Broadly accepted JSON/ATOM format on the wire
• What OData Is Not:
• Not to replace native or direct data access interface, e.g. ODBC/TDS
for SQL
• Not to replace highly specialized BI technologies like XMLA

OData Status
• OData v4 to be standardized in Feb. in OASIS
• http://docs.oasis-open.org/odata/new-in-odata/v4.0/cn01/new-in-odata-v4.0-
cn01.html
• ODL 6.2
• http://blogs.msdn.com/b/odatateam/archive/2014/04/14/odl-6-2-release-
announcement.aspx
• Web API OData 6.1
• http://blogs.msdn.com/b/odatateam/archive/2014/03/21/odata-6-1-and-odata-
client-6-1-are-now-shipped.aspx
• WCF Data Services moved to OSS
• http://blogs.msdn.com/b/odatateam/archive/2014/03/27/future-direction-of-wcf-
data-services.aspx
http://odata.org/

Technology Basics
Client Server
OData Service
OData
Protocol
Library
OData
Data
Model
Library
Data
Source
Technology .NET
OData Data Model Library Microsoft.odata.edm.dll
OData Protocol Library Microsoft.odata.core.dll
OData Service WCF Data Service/ Web API/ User’s own service
OData Client Library Microsoft.odata.client.dll
Code Generator T4 / item template
OData
Protocol
Library
OData
Data
Model
Library
OData Client
Library
OData
Protocol
Library
OData
Data
Model
Library

How to build client to consume
OData
Business Logic
Dev OData
Service
Metadata request
Use Code Generatror to generate client class
Client
Application
Account account = TestClientContext.Accounts.Where(account => account.AccountID
== 110).Single();
account.Country=”US”;
TestClientContext.UpdateObject(account);
TestClientContext.SaveChanges();
Code Files(Account.cs/
TestClientContext.cs)
Microsoft.odata.client.dll
The client dll will generate the request
based on the property change on the Account object
Get http://localhost:8080/OData/Accounts(110)
Patch http://localhost:8080/OData/Accounts(110)

What’s in Microsoft.OData.Client.dll
•Deserialize/Serialize OData payload
• Using API provided by Microsoft.OData.Core.dll
•Request Generator/LINQ to URL
•Entity Tracker
•Batch support

OData Data Model Library
• OData is based on the Entity Data Model (EDM):
• EDM presents information in a way which is familiar to
many developers dealing with data today making it
easy for them to understand and use.
• Data provider can use OData Data Model Library to
create the EDM model of the data they want to
expose. The client can consume the data based on
the EDM model that exposed by service and figure
out the relationship between entities.

EDM Example
Entity Container
Entity set
(Categories)
Category
CategoryId Product
Entity set
(Products)
Product
ProductId Description
Navigation property binding

EDM Example – Cont.
• <?xml version="1.0" encoding="utf-8"?>
<edmx:Edmx Version="4.0" xmlns:edmx="http://docs.oasis-open.org/odata/ns/edmx">
<edmx:DataServices>
<Schema Namespace="Microsoft.Test.OData.Services.ODataWCFService" xmlns="http://docs.oasis-open.org/odata/ns/edm">
<EntityType Name="Category">
<Key>
<PropertyRef Name="CategoryId" />
</Key>
<Property Name="CategoryId" Type="Edm.String" Nullable="false" />
<Property Name="Name" Type="Edm.String" Nullable="false" />
<NavigationProperty Name="Product" Type="Microsoft.Test.OData.Services.ODataWCFService.Product" Nullable="false" />
</EntityType>
<EntityType Name="Product">
<Key>
<PropertyRef Name="ProductId" />
</Key>
<Property Name="ProductId" Type="Edm.String" Nullable="false" />
<Property Name="Name" Type="Edm.String" Nullable="false" />
<Property Name="Desciption" Type="Edm.String" Nullable="false" />
</EntityType>
<EntityContainer Name="ServiceContainer">
<EntitySet Name="Categories" EntityType="Microsoft.Test.OData.Services.ODataWCFService.Category">
<NavigationPropertyBinding Path="Product" Target="Products" />
</EntitySet>
<EntitySet Name="Products" EntityType="Microsoft.Test.OData.Services.ODataWCFService.Product">
</EntitySet>
</EntityContainer>
</Schema>
</edmx:DataServices>
</edmx:Edmx>

EDM Example – Cont.
• Category Entity:
• http://localhost/odata/Categories(1)
• Product under this category
• http://localhost/odata/Categories(1)/Product
• Through navigation binding defined in the Categories
and the navigation property defined in the Category,
target entity set Products can be found
• Entity product can be located in entity set Products

OData Protocol Library
• Deserialize/Serialize payload
• JSON
• Full metadata level
– {
– "@odata.context":"http://localhost:50671/ODataService.svc/OData/$metadata#Products/$entity",
– "@odata.id":"http://localhost:50671/ODataService.svc/OData/Products(5)",
– "@odata.editLink":"http://localhost:50671/ODataService.svc/OData/Products(5)",
– "ProductID":5,
– "Name":"Cheetos",
– "Description":"Cheese curl"
– }
• Minimal metadata level
– Writer only writes the necessary metadata
– Reader will auto complete the metadata during reading
– {
– "@odata.context":"http://localhost:50671/ODataService.svc/OData/$metadata#Products/$entity",
– "ProductID":5,
– }
• No metadata level
– Data only
– {
– "ProductID":5,
– }
• ATOM

OData Protocol Library
• Targeting the target resource based on the URI
• $top=n: Returns only the first n entities in an entity set (or in Atom terms,
the first n entries in a feed)
• $skip=n: Skips the first n entities in an entity set. Using this option lets a
client retrieve a series of distinct pages on subsequent requests
• $format: Determines whether data should be returned in JSON or the XML-
based Atom/AtomPub format
• $orderby=: Orders results, in ascending or descending order, by the value
of one or more properties in those results
• $filter=: Returns only entities that match the specified expression
• $select=: Returns only the specified properties in an entity
• $expand=: Returns the navigation property in an entity
URI Parser

OData Protocol Library – Cont.
• http://services.odata.org/V3/Northwind/Northwind.svc/Order_Details?$top=5
&$select=OrderID,ProductID&$skip=1&$filter=OrderID gt 10248
• Parsed result of request URI as an ODataUri object
• TopCount
• SkipCount
• SelectExpandClause
• List<SelectedItem>
– PathSelectionItem
» Path=OrderID
– PathSelectionItem
» Path=ProductID
• FilterClause
• FilterExpression

WebApi.OData: Overview
•An OData service library
•Build upon a lightweight http stack
•Be part of ASP.NET RESTful framework
•Selective query ability
•Another option to build OData service

Simple way to build OData Service
•No need to know the details of OData Protocol
•POCO (Plain Old CLR Object) model
•ODataConventionModelBuilder: 3 lines of code
var builder = new ODataConventionModelBuilder();
builder.EntitySet<Product>("Products");
IEdmModel model = builder.GetEdmModel();
•ODataController: VS2013 scaffolding

Web API OData Architecture Diagram
Message Handler
Controller Selection
ODataController
Action
Action Filter
MapODataRoute*GetEdmModelModel builderEdm Lib
Spatial Lib
Formatter
OData Lib
Serialize
Deserialize
Query
Entity Framework
DbContext
DbSet
Action Filter
Formatter Model Binder QueryOption
Action Selection
Type system
HttpRequestMessage
HttpResponseMessage

Components
• Model builder
• ODataModelBuilder
• ODataConventionModelBuilder (a 3 lines of code approach)
• Query
• ODL Semantic AST -> LINQ Expression (IQueryable) -> LINQ to * (Entities,
Objects…)
• Routing
• Conventional
• Attribute route
• Formatter
• Serializer: CLR type / typeless -> OData*Value
• Deserializer: OData*Value -> CLR type / typeless

Routing Examples
// Metadata routes to support $metadata and code generation in the
// WCF Data Service client.
configuration.Routes.MapHttpRoute(
ODataRouteNames.Metadata,
"$metadata",
new { Controller = "ODataMetadata", Action = "GetMetadata" }
);
ODataRouteNames.ServiceDocument,
"",
new { Controller = "ODataMetadata", Action = "GetServiceDocument" }
);

Routing Examples…
// Relationship routes (notice the parameters is {type}Id not id,
// this avoids colliding with GetById(id)).
// This code handles requests like ~/ProductFamilies(1)/Products
ODataRouteNames.PropertyNavigation,
"{controller}({parentId})/{navigationProperty}");
// Route for manipulating links, the code allows people to create and
// delete relationships between entities
ODataRouteNames.Link,
"{controller}({id})/$links/{navigationProperty}");

Routing Examples…
// Routes for urls both producing and handling URLs
// like: ~/Product(1), ~/Products() and ~/Products
ODataRouteNames.GetById,
"{controller}({id})");
ODataRouteNames.DefaultWithParentheses,
"{controller}()");
ODataRouteNames.Default,
"{controller}");

Model Builder
• ODataConventionModelBuilder
• Use reflection and conventions to generate an Edm model
• Reflection
• Type
• PropertyInfo
• MethodInfo
• Conventions
• AttributeConvention
• AttributeEdmTypeConvention: [DataContract]
• AttributeEdmPropertyConvention:
• [Key]
• [DataMember]
• [IgnoreDataMember]
• [Required]
• [ConcurrencyCheck]…

ODataModelBuilder
• Take full control
var builder = new ODataModelBuilder();
var products =
builder.EntitySet<Product>("Products");
var product = products.EntityType;
product.HasKey(p => p.ID);
product.Property(p => p.Name);
var rate = product.Action("Rate");
rate.Parameter<int>("Rating");
rate.Returns<double>();
• EntitySetConfiguration
• EntityTypeConfiguration
• PropertyConfiguration
• ProcedureConfiguration
• ParameterConfiguration

Query
• /Products/?$filter=Name eq ‘abc’
• One key differentiator than other Web API implementations
• QueryableAttribute
[Queryable]
public IQueryable<Product> GetProducts()
{
return db.Products;
}
• => ODataQueryOptions
public IEnumerable<Product> GetProducts(ODataQueryOptions options)
{
return options.ApplyTo(db.Products) as IEnumerable<Product>;
}
• FilterQueryOption -> FilterBinder:
• Convert OData AST FilterClause’s QueryNode to Linq Expression

Routing
• IODataRoutingConvention
• string SelectController(ODataPath odataPath, HttpRequestMessage request);
• string SelectAction(ODataPath odataPath, HttpControllerContext controllerContext,
ILookup<string, HttpActionDescriptor> actionMap);
• Convention based route:
• EntitySetRoutingConvention
• EntityRoutingConvention
• ActionRoutingConvention
• FunctionRoutingConvention
• NavigationRoutingConvention
• PropertyRoutingConvention
• Attribute based route:
• AttributeRoutingConvention
• ODataRouteAttribute
• MapODataRoute

Formatter
• Why does webapi.odata need to handle serialization and
deserialization?
• ODL handles OData object model to Payload
• Web API handles POCO to OData OM
• The hook:
[ODataFormatting]
public abstract class ODataController : ApiController
• ODataFormattingAttribute
• Inserts the ODataMediaTypeFormatters into the HttpControllerSettings.Formatters
collection.
• Attaches the request to the OData formatter instance.
• ODataMediaTypeFormatter.Create()
• ODataSerializerProvider / ODataDeserializerProvider
• OData*Serializer / OData*Deserializer

Demo
Build an OData Web API application

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Building RESTfull Data Services with WebAPI

Building RESTfull Data Services with WebAPI

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