Define entity relations

Applies To: # OData core lib v7 supported OData Core Lib V7

Entity relations are defined by navigation properties in entity data models. Adding a navigation property to an entity type using EdmLib APIs is as simple as adding a structural property shown in previous sections. EdmLib supports adding navigation properties targeting an entity set in the entity container or a contained entity set belonging to a navigation property.

This section shows how to define navigation properties using EdmLib APIs. We will use and extend the sample from the previous section.

Add a navigation property Friends

In the SampleModelBuilder.cs file, insert the following code into the SampleModelBuilder class:

namespace EdmLibSample
{
    public class SampleModelBuilder
    {
        ...
        private EdmNavigationProperty _friendsProperty;
        ...
        public SampleModelBuilder BuildCustomerType()
        {
            ...
            _customerType.AddStructuralProperty("Address", new EdmComplexTypeReference(_addressType, isNullable: false));
#region     !!!INSERT THE CODE BELOW!!!
            _friendsProperty = _customerType.AddUnidirectionalNavigation(
                new EdmNavigationPropertyInfo
                {
                    ContainsTarget = false,
                    Name = "Friends",
                    Target = _customerType,
                    TargetMultiplicity = EdmMultiplicity.Many
                });
#endregion
            _model.AddElement(_customerType);
            return this;
        }
        ...
        public SampleModelBuilder BuildCustomerSet()
        {
            _customerSet = _defaultContainer.AddEntitySet("Customers", _customerType);
#region     !!!INSERT THE CODE BELOW!!!
            _customerSet.AddNavigationTarget(_friendsProperty, _customerSet);
#endregion
            return this;
        }
        ...
    }
}

This code:

• Adds a navigation property Friends to the entity type Customer;
• Sets the ContainsTarget property to false since this property has no contained entities but targets one or more Customer entities in the entity set Customers;
• Sets the TargetMultiplicity property to EdmMultiplicity.Many, indicating that one customer can have many orders. Other possible values include ZeroOrOne and One.

Add entity Type Order and entity set Orders

Just as how we added the entity set Customers, we first add an entity type Order and then the entity set Orders.

In the SampleModelBuilder.cs file, insert the following code into the SampleModelBuilder class:

namespace EdmLibSample
{
    public class SampleModelBuilder
    {
        ...
        private EdmEntityType _orderType;
        ...
        private EdmEntitySet _orderSet;
        ...
        public SampleModelBuilder BuildOrderType()
        {
            _orderType = new EdmEntityType("Sample.NS", "Order");
            _orderType.AddKeys(_orderType.AddStructuralProperty("Id", EdmPrimitiveTypeKind.Int32, isNullable: false));
            _orderType.AddStructuralProperty("Price", EdmPrimitiveTypeKind.Decimal);
            _model.AddElement(_orderType);
            return this;
        }
        ...
        public SampleModelBuilder BuildOrderSet()
        {
            _orderSet = _defaultContainer.AddEntitySet("Orders", _orderType);
            return this;
        }
        ...
    }
}

In the Program.cs file, insert the following code into the Main() method:

namespace EdmLibSample
{
    class Program
    {
        public static void Main(string[] args)
        {
            var builder = new SampleModelBuilder();
            var model = builder
                .BuildAddressType()
                .BuildCategoryType()
#region         !!!INSERT THE CODE BELOW!!!
                .BuildOrderType()
#endregion
                .BuildCustomerType()
                .BuildDefaultContainer()
#region         !!!INSERT THE CODE BELOW!!!
                .BuildOrderSet()
#endregion
                .BuildCustomerSet()
                .GetModel();
            WriteModelToCsdl(model, "csdl.xml");
        }
    }
}

Add navigation properties Purchases and Intentions

In the SampleModelBuilder.cs file, insert the following code into the SampleModelBuilder class:

namespace EdmLibSample
{
    public class SampleModelBuilder
    {
        ...
#region !!!INSERT THE CODE BELOW!!!
        private EdmNavigationProperty _purchasesProperty;
        private EdmNavigationProperty _intentionsProperty;
#endregion
        ...
        public SampleModelBuilder BuildCustomerType()
        {
            ...
#region     !!!INSERT THE CODE BELOW!!!
            _purchasesProperty = _customerType.AddUnidirectionalNavigation(
                new EdmNavigationPropertyInfo
                {
                    ContainsTarget = false,
                    Name = "Purchases",
                    Target = _orderType,
                    TargetMultiplicity = EdmMultiplicity.Many
                });
            _intentionsProperty = _customerType.AddUnidirectionalNavigation(
                new EdmNavigationPropertyInfo
                {
                    ContainsTarget = true,
                    Name = "Intentions",
                    Target = _orderType,
                    TargetMultiplicity = EdmMultiplicity.Many
                });
#endregion
            _model.AddElement(_customerType);
            return this;
        }
        ...
        public SampleModelBuilder BuildCustomerSet()
        {
            _customerSet = _defaultContainer.AddEntitySet("Customers", _customerType);
            _customerSet.AddNavigationTarget(_friendsProperty, _customerSet);
#region     !!!INSERT THE CODE BELOW!!!
            _customerSet.AddNavigationTarget(_purchasesProperty, _orderSet);
#endregion
            return this;
        }
    }
}

This code:

• Adds a Purchases navigation property targeting one or more settled orders in the entity set Orders;
• Adds an Intentions navigation property targeting a contained entity set of unsettled orders that are not listed in the entity set Orders.

Run the sample

Build and run the sample. Then open the file csdl.xml under the output directory. The content of it should look like the following:

References

[Tutorial & Sample] Containment is Coming with OData V4.