Enumeration is a very common data type in various data models. Enumeration types are useful means to represent data that needs to support certain programmatic options (such as the ability to detect one or more options are selected). OData v4 now supports Enumeration types, along with Primitive types, Complex types, and Entity types. And we expect there will be heavy usage of them.<\/p>\n
Let\u2019s look at an example. Suppose we have an entity type called Product<\/strong>, and we want to have a property member that stores the color of the product. We could use a string type property, but an enumeration type property would look better. We can define an enumeration type Color<\/strong>, and it contains members like Red<\/em>, Green<\/em>, Blue<\/em>, etc. In Product definition we can define a member property called PackageColor<\/em>, whose type is Color<\/strong>. Now we can assign color values to PackageColor<\/em>. To get all the products that are in Green<\/em> color, we can send a request like \u201c\/svc\/Products?$filter=PackageColor eq Namespace.Color\u2019Green<\/span>\u2019\u201d.<\/p>\n An enumeration type can be defined with \u201cIsFlags=true\u201d, meaning that the members can be combined using bitwise; otherwise the members are intended to be exclusive. The Color<\/strong> type in the example above is defined with \u201cIsFlags=false\u201d, as we don\u2019t want its members to be combined (we don\u2019t allow a color to be both green and blue). Here another example is an enumeration type called AccessLevel<\/strong>, which indicates the rights on some resource. AccessLevel<\/strong> has some members Like: None, Read, Write, Execute<\/em>. In Product type we have another property named UserAccess<\/em> which is of AccessLevel<\/strong> type. We can assign combined values to UserAccess<\/em>, such as \u201cRead, Write\u201d. And if we want to get all the products that we have Read<\/em> and Write<\/em> access to, we can send a query like \u201c\/svc\/Products?$filter=UserAccess has Namespace.AccessLevel\u2019Read, Write\u2019<\/span>\u201d. The \u201chas\u201d operator is evaluated in a bitwise way. That means UserAccess may contain more bits than the value on the right of the operator.<\/p>\n How to use Enumeration types in your OData service? The following part will give the elaborated steps, as well as some code snippets to help you understand. You can get the complete sample code here<\/a>.<\/p>\n On server side, you need to first build an EDM model that supports your scenario with enumeration types. With the model ready, your service needs to respond to client requests by writing the correct payload which may have enumeration type values in it. The second step is called serialization. Let\u2019s look at the details.<\/p>\n 1. <\/strong>Build the EdmModel.<\/strong><\/span><\/p>\n To use Enum type, you need to first define your Enum types in EdmModel. The enum type can be defined with “IsFlags=true” or \u201cIsFlags=false\u201d. The absence of the IsFlags attribute implies the default behavior: the same as “IsFlags=false”.<\/p>\n The following code defines two Enum types: Color<\/strong> and AccessLevel<\/strong>, and an entity type Product<\/strong> which has two properties UserAccess<\/em> and PackageColor<\/em>, of type AccessLevel<\/strong> and Color<\/strong> respectively.<\/p>\n