How to set up a pointer field

In the field definition setting screen, we can create a new field definition with type = Pointer. 

Then we can define the entity type of that pointer in the Entity section.

In this sample pointer, Pages have been selected as Entity and the Multi-select option has been ticked. This is what it looks like after we add it to the article-page template:

If we click Add we'll see the page-selection dialog. This dialog will list all the pages that we have in the system, under each channel:

Then we can select multiple alternatives and click OK. The selection will be stored in that field's value: 

There're two types of PointerItem:

• PointerPageItem which has both EntitySystemId and ChannelSystemId that link to a page on the website.
• The normal PointerItem which has only EntitySystemId.

This is an example where we create two pointer fields with both types of PointerItem:

public void PoiterFieldTest()
{
    //Create pointer-field definition
    var pointerFieldDefinition =
        new FieldDefinition<CustomerArea>(this.UniqueString(), SystemFieldTypeConstants.Pointer)
        {
            Option =  new PointerOption()
            {
                EntityType = PointerTypeConstants.CustomersGroup,
                MultiSelect = true
            }
        };
    _fieldDefinitionService.Create(pointerFieldDefinition);

    //Create pointer-field definition
    var pagePointerFieldDefinition =
        new FieldDefinition<CustomerArea>(this.UniqueString(), SystemFieldTypeConstants.Pointer)
        {
            Option = new PointerOption()
            {
                EntityType = PointerTypeConstants.WebsitesPage,
                MultiSelect = true
            }
        };
    _fieldDefinitionService.Create(pagePointerFieldDefinition);

    // Create group field template
    var sampleGroupFieldTemplate = new GroupFieldTemplate(this.UniqueString())
    {
        FieldGroups = new[]
        {
            new FieldTemplateFieldGroup()
            {
                Id = "General",
                Collapsed = false,
                Fields =
                {
                    pointerFieldDefinition.Id,
                    pagePointerFieldDefinition.Id
                }
            }
        }
    };
    _fieldTemplateService.Create(sampleGroupFieldTemplate);
    
    //prepare pointer field data 
    var innerData1 = new PointerItem { EntitySystemId = Guid.NewGuid()};
    var innerData2 = new PointerItem { EntitySystemId = Guid.NewGuid() };
    var innerData3 = new PointerPageItem { EntitySystemId = Guid.NewGuid(), ChannelSystemId = Guid.NewGuid()};
    var innerData4 = new PointerPageItem { EntitySystemId = Guid.NewGuid(), ChannelSystemId = Guid.NewGuid() };

    //Create a sample static group and assign pointer field value to it:
    var sampleGroup = new StaticGroup(sampleGroupFieldTemplate.SystemId, this.UniqueString());
    sampleGroup.Fields.AddOrUpdateValue(pointerFieldDefinition.Id, new[] { innerData1, innerData2 });
    sampleGroup.Fields.AddOrUpdateValue(pagePointerFieldDefinition.Id, new[] { innerData3, innerData4 });
    _groupService.Create(sampleGroup);

    //Retrieve the group we've created and extract the multifield value
    var savedGroup = _groupService.Get<StaticGroup>(sampleGroup.SystemId);
    var pointerFieldValue = savedGroup.Fields.GetValue<IList<PointerItem>>(pointerFieldDefinition.Id);
    var pagePointerFieldValue = savedGroup.Fields.GetValue<IList<PointerItem>>(pagePointerFieldDefinition.Id).OfType<PointerPageItem>().ToList();

    //Asserts
    if(pointerFieldValue != null) 
    {
        var count = pointerFieldValue.Count; //Should be 2
        var entityId1 =  pointerFieldValue.First().EntitySystemId; // Should equal innerData1.EntitySystemId
        var entityId2 =  pointerFieldValue.Last().EntitySystemId;  // Should equal innerData2.EntitySystemId  
    }
    if(pagePointerFieldValue != null)
    {
        var count = pointerFieldValue.Count; //Should be 2
        var entityId1 =  pagePointerFieldValue.First().EntitySystemId; // Should equal innerData3.EntitySystemId
        var channelId1 =  pagePointerFieldValue.First().ChannelSystemId; // Should equal innerData3.ChannelSystemId
        var entityId2 =  pagePointerFieldValue.Last().EntitySystemId;  // Should equal innerData4.EntitySystemId
        var channelId2 =  pagePointerFieldValue.Last().ChannelSystemId;  // Should equal innerData4.ChannelSystemId  
    }
}