Consumed OData Service Requirements

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1 Introduction

This document describes the requirements for an OData service that is going to be consumed. These requirements are not further verified at runtime and expected to hold. If these requirements are not met, errors may result.

2 Requirements for a Consumed OData Service

The requirements for a consumed OData service used in a Mendix app are the following:

  • The OData service must be either an OData v3 service returning Atom XML, or an OData v4 service returning either Atom XML or JSON
  • It should support queries on the OData feed, including $filter, $orderby, $top, $skip, $expand, and $count (or $inlinecount)

3 Requirements on the Service Entities and Attributes

This section describes the features of a consumed OData service that are supported in Mendix apps. These features are checked before an external entity is used in the domain model.

3.1 Entities

Vocabulary annotations can be used in a service to indicate features that are not supported. The following vocabulary annotations are recognized for entity sets:

  • Countable – an entity set marked as Countable="false" prevents the user from adding the entity to the app
  • Filterable – an entity set marked as Filterable="false" sets all properties as non-filterable
  • Sortable – an entity set marked as Sortable="false" sets all properties as non-sortable
  • Marking an entity set as Filterable="false" and Sortable="false" sets all properties as non-filterable and non-sortable; marking properties with the NonFilterableProperties annotation or the NonSortableProperties annotation sets specific attributes as non-filterable or non-sortable
  • Updatable - an entity marked as Updatable="true" with DeltaUpdateSupported="true" and UpdateMethod="2" will make the entity updatable in the domain model. That means, for instance, that you can model pages that change attributes values and associated objects, and that you can use the entity in the Change object action. For updatable entities, the annotations NonUpdatableProperties and NonUpdatableNavigationProperties can be used to list the (navigation)properties that cannot be updated.

An entity can only be used when it is accessible through an entity set.

Furthermore, an entity can only be used if it is uniquely identifiable with a key. The key can consist of one or more properties, as long as the following conditions are met:

  • The properties cannot be nullable (so they must have isNullable="false" specified).
  • Only the following types are allowed: Byte, SByte, Int16, Int32, Int64, Boolean, Decimal, Single, Double, and String.
  • If the type of a key property is String, it must have a limited (maximum) length specified. This is because not all databases support indexes on strings of unlimited length. It is sufficient if a MaxLength is specified in the contract. However, if a MaxLength is not specified in the contract, and you know that the string is limited in length, you can still use the entity by specifying the maximum length of the attribute in the the domain model.

3.2 Attributes

Attribute types have to be primitive (not complex, collections, or enumerations). The types of the attributes in your app will be based on the types of the attributes in the OData metadata, as given in the following table:

OData Type Mendix Type
Binary Binary (but see 3.4)
Boolean Boolean [1]
Byte, SByte, Int16, Int32 Integer
DateTime, DateTimeOffset, Time Date/time
Decimal, Double, Single Decimal [2]
Int64 Long
String, Guid String
(Other) (Ignored)

[1] In Mendix, Booleans cannot be null. If the service returns null, the value will be false in Mendix.
[2] Decimal values outside of the range of a Mendix decimal are currently not supported. If the service returns a value outside of the range, there will be an error.

3.3 Generalizations

The consumed OData service does not support importing generalizations and specializations. This means that the Published OData service contract from the originating app will show specializations as discrete entities which will include the attributes of the generalization along with the attributes of the specialized entity.

This means that when you are consuming a Mendix OData endpoint, it is not necessary to consume both a generalization and its specialization. The specialization will now be an entity with all the attributes and associations of the generalization.

Associations to the generalizations with other exposed entities in the published OData service will be included for the now discrete “specialized” entities.

3.4 Binary Attributes

The binary data format is supported in the form of media entities. When a media entity is dragged into the domain model, a corresponding external entity is created. The entity will have a contents attribute with the binary data.

Currently, the binary data can only be accessed by Java actions.

3.5 Associations

An OData v3 association can only be used if it has two ends.

An OData v4 navigation property can only be used as an association if it has a partner.

4 Data Hub License

4.1 Limitations

Mendix Data Hub is a separately licensed product.

Without a license, an app can retrieve a total of 1000 OData objects per day for each runtime instance. After that limit is exceeded, an error occurs when users try to retrieve more data. The number of consumed objects per day is reset at midnight in the time zone of the Mendix Runtime scheduler (which can be defined in the Scheduled Event Time Zone of the App Settings).

With a Data Hub license, apps are not limited in retrieving OData objects.

Contact your Mendix Admin to find out what type of Data Hub license your organization has.

4.1 Limitation Errors

For each call, the app instance logs how many objects it has retrieved and how many are left within the license limitation. Once the limit of a 1000 objects has been reached, two different statements are logged.

  • On the info level, the following statement is logged when the limit is reached: "Exceeded the daily limit. Retrieved $delta objects, which would increase the counter to $newCount (of max $max per day)."
  • On the error level, the following statement is logged when the limit is reached: "The limit of $max objects has been reached."