How To Have Multiple Entries For Custom Entity?

In our Dynamics CRM online custom project - we've the default ACTIVITIES tab in a custom entity named DocProject's form ACTIVITIES is able to take multiple entries. Also, there is

Solution 1:

In order to have the associated activity grid like the one in the DocProject entity, you need to enable the option Activities when you're creating the entity (this option can't be changed after the entity is created). This option will create the association with the activities entities and allow you to track all the related phone calls, task, etc.

I think that the problem that you're having is that you defined the DocProjectActivities as an activity entity and therefore you can't have this kind of relationship with the other activities entities. I recommend you to take a look to the differences between Entities and Activity Entities.

Solution 2:

Do you mean you need multiple docprojectactivities on the form where you have the activities? You need to create a 1:n relationship between the form and the docprojectactivities and add the subgrid on that form allowing you to create multiple records for the docprojectactivities. A lookup field is the '1' side of the 1:n relationship and thus the wrong direction.

Go to docprojectactivities, add a new field type relationship towards the entity you are working on. Save and publish.

Now go back to the form designer of the entity you need the entries on and go to the tab 'insert'.

Click on sub-grid and select only related records docprojectactivities (entity you are working on)

Solution 3:

If you want your custom entity to work as an activity entity, you should have selected "Define as an activity entity" when you created it.

You cannot make a normal lookup field to multiple entities (with the exception being the possibility of creating Customer fields that was introduced in 2016.1).