Removing references to cardinality/many without deleting the entity

[jamesnyika]

Datascript 0.18.7

I have the following schema . Events can have multiple contacts associated with them but I want contacts to remain as truly independent entities

 ;;=========CONTACT===========
   :contact/name           {:db/doc    "First and Lastname of the contact"
                            :db/unique :db.unique/identity}
   :contact/firstname      {:db/cardinality :db.cardinality/one
                            :db/doc         "Contact firstname"}
   :contact/lastname       {:db/cardinality :db.cardinality/one
                            :db/doc         "Contact lastname"}
   :contact/type           {:db/cardinality :db.cardinality/one
                            :db/doc         "Contact type - ref to contact type lookup"}
   :contact/mobilephone    {:db/doc "Contact Mobile Phone number"}

   :event/contacts          {:db/doc         "Event Contact - ref to Contact"
                            :db/isComponent true
                            :db/cardinality :db.cardinality/many
                            :db/valueType   :db.type/ref
                            }

I then load it up with data and it looks something like this

{:event/endtime #inst "2019-10-12T00:30:00.000-00:00",
  :event/desc "Corp Earnings Event Baltimore, MD",
  :event/contacts
  [{:db/id 63, :contact/name "Janet Lansdale"}
   {:db/id 64, :contact/name "Nina Simone"}],
  :event/starttime #inst "2019-10-11T16:31:00.000-00:00",
  :db/id 62,
  :event/status [:lookup/name "QUOTING"]}

When I want to dissoc one of these contacts, I run a transact with this same data structure but I remove one of the entries ..eg. Nina Simone as shown below

{:event/endtime #inst "2019-10-12T00:30:00.000-00:00",
  :event/desc "Corp Earnings Event Baltimore, MD",
  :event/contacts
  [{:db/id 63, :contact/name "Janet Lansdale"}],
  :event/starttime #inst "2019-10-11T16:31:00.000-00:00",
  :db/id 62,
  :event/status [:lookup/name "QUOTING"]}

or to remove them completely I try

{:event/endtime #inst "2019-10-12T00:30:00.000-00:00",
  :event/desc "Corp Earnings Event Baltimore, MD",
  :event/contacts [],
  :event/starttime #inst "2019-10-11T16:31:00.000-00:00",
  :db/id 62,
  :event/status [:lookup/name "QUOTING"]}

but submitting these transactions does not remove them.

Question: How do you run a transaction that will dissoc the contacts from the events but NOT delete them.

Interestingly, as long as I add more, there is no problem but not going the other way ?

[tonsky]

Just remove :db/isComponent true from the schema. The main thing isComponent does is cascade updates. Basically it says "this thing is part of the other thing and its lifetime is tied to the bigger thing"

[jamesnyika]

I will try that out and see if I can verify it. Once I have a response I will post back here. Thank you for the explanation..

[jamesnyika]

@tonsky Unless I'm messing up, I am actually not getting the result expected.

Datascript 0.18.7
Using re-posh , reagent and re-frame in a React Native Environment with Expo
I did not post the seed setup data but let me know if you need to see it...

Schema

..
;;----ADDRESSES----
  :address/name           {:db/doc    "(PK) A name for this address"
                           :db/unique :db.unique/identity}
  :address/type           {:db/cardinality :db.cardinality/many
                           :db/valueType   :db.type/ref
                           :db/doc         "Address type - can be home, billing, office or all of these"}
  :address/main           {:db/doc "is this the main address"}
  :address/line1          {:db/doc "line 1 of the address"}
  :address/line2          {:db/doc "line 2 of the address"}
  :address/city           {:db/doc "String name of the city"}
  :address/locality-state {:db/doc "state/province/locality for this address"}
  :address/postalcode     {:db/doc "postal code for mailings"}
  :address/country        {:db/doc "country name for address"}
;;=========CONTACT===========
   :contact/name           {:db/doc    "First and Lastname of the contact"
                            :db/unique :db.unique/identity}
   :contact/firstname      {:db/cardinality :db.cardinality/one
                            :db/doc         "Contact firstname"}
   :contact/lastname       {:db/cardinality :db.cardinality/one
                            :db/doc         "Contact lastname"}
   :contact/type           {:db/cardinality :db.cardinality/one
                            :db/doc         "Contact type - ref to contact type lookup"}
   :contact/mobilephone    {:db/doc "Contact Mobile Phone number"}

;;=========EVENT=======
   :event/name             {:db/doc    "(PK) Name of this Event"
                            :db/unique :db.unique/identity}
   :event/type             {:db/doc       "Type of event - reference to lookup value"
                            :db/valueType :db.type/ref}
   :event/customer        {:db/doc    "Customer for whome this event is being done"
                           :db/valueType   :db.type/ref
                           :db/cardinality :db.cardinality/one
                           }
   :event/location         {:db/doc       "Where is the event taking place - ref to location"
                            :db/cardinality :db.cardinality/one
                            :db/valueType :db.type/ref}
   :event/contacts          {:db/doc         "Event Contact - ref to Contact"
                            :db/cardinality :db.cardinality/many
                            :db/valueType   :db.type/ref
                            }
 
   }

Begin: Read from db

{:event/endtime #inst "2019-10-12T00:30:00.000-00:00",
  :event/desc "Corp Earnings Event Baltimore, MD",
  :event/contacts
  [{:db/id 55,
    :contact/email "janet.lansdale@google.com",
    :contact/firstname "Janet",
    :contact/lastname "Lansdale",
    :contact/mobilephone "+12023938484",
    :contact/name "Janet Lansdale",
    :contact/type {:key 1, :label "Contact de facturation"}}
   {:db/id 56,
    :contact/email "nina@gmail.com",
    :contact/firstname "Nina",
    :contact/lastname "Simone",
    :contact/mobilephone "+1202575484",
    :contact/name "Nina Simone",
    :contact/type {:key 1, :label "Contact de facturation"}}],
  :event/starttime #inst "2019-10-11T16:31:00.000-00:00",
  :event/location
  {:address/type [{:db/id 38}],
   :address/line1 "Surinamestraat 27",
   :address/country -101,
   :address/postalcode "2585",
   :address/main true,
   :label "St Regis Washington DC",
   :address/locality-state "GJ",
   :db/id 37,
   :address/name "St Regis Washington DC",
   :address/city "Rotterdam"},
  :app/active true,
  :event/customer
  {:db/id 51,
   :label "Google Corp.",
   :customer/name "Google Corp.",
   :customer/type {:db/id 52}},
  :db/id 61,
  :event/type
  {:db/id 44,
   :lookup/locale :en_US,
   :lookup/name "Company Party",
   :lookup/type {:db/id 41},
   :lookup/value :corporateparty},
  :event/name "Tellemann Corporate Party",
... (other fields) 

I then modify this on the UI and submit the following map to the transact! function

Map passed to transact! just before execution

{:event/endtime #inst "2019-10-12T00:30:00.000-00:00",
  :event/desc "Corp Earnings Event Baltimore, MD",
  :event/contacts [{:contact/name "Nina Simone", :db/id 56}],
  :event/starttime #inst "2019-10-11T16:31:00.000-00:00",
  :event/location
  {:address/type [{:db/id 35} {:db/id 36}],
   :address/line2 "# 45",
   :address/line1 "Surinamestraat 27",
   :address/country -101,
   :address/postalcode "2585",
   :address/main true,
   :label "CC Billing Address",
   :address/locality-state "GJ",
   :db/id 34,
   :address/name "CC Billing Address",
   :address/city "Rotterdam"},
  :app/active true,
  :event/customer
  {:db/id 53,
   :label "Apple Corp.",
   :customer/name "Apple Corp.",
   :customer/type {:db/id 54}},
  :db/id 61,
  :event/type
  {:db/id 45,
   :label "Fundraiser",
   :lookup/locale :en_US,
   :lookup/name "Fundraiser",
   :lookup/type {:db/id 41},
   :lookup/value :fundraiser},
  :event/name "Tellemann Corporate Party",
... (other fields)

Notice

• I submitted a change to the customer name entity (53)
• I submitted a change to entity 45 at the bottom
• I submitted a change to the address (entity 34)
• I submitted a change to the number of event/contacts (less by 1) <--this is the key one to watch

Results After Transact!

{:event/endtime #inst "2019-10-12T00:30:00.000-00:00",
  :event/desc "Corp Earnings Event Baltimore, MD",
  :event/contacts
  [{:db/id 55,
    :contact/email "janet.lansdale@google.com",
    :contact/firstname "Janet",
    :contact/lastname "Lansdale",
    :contact/mobilephone "+12023938484",
    :contact/name "Janet Lansdale",
    :contact/type {:key 1, :label "Contact de facturation"}}
   {:db/id 56,
    :contact/email "nina@gmail.com",
    :contact/firstname "Nina",
    :contact/lastname "Simone",
    :contact/mobilephone "+1202575484",
    :contact/name "Nina Simone",
    :contact/type {:key 1, :label "Contact de facturation"}}],
  :event/starttime #inst "2019-10-11T16:31:00.000-00:00",
  :event/location
  {:address/type [{:db/id 35} {:db/id 36}],
   :address/line2 "# 45",
   :address/line1 "Surinamestraat 27",
   :address/country -101,
   :address/postalcode "2585",
   :address/main true,
   :label "CC Billing Address",
   :address/locality-state "GJ",
   :db/id 34,
   :address/name "CC Billing Address",
   :address/city "Rotterdam"},
  :app/active true,
  :event/customer
  {:db/id 53,
   :label "Apple Corp.",
   :customer/name "Apple Corp.",
   :customer/type {:db/id 54}},
  :db/id 61,
  :event/type
  {:db/id 45,
   :label "Fundraiser",
   :lookup/locale :en_US,
   :lookup/name "Fundraiser",
   :lookup/type {:db/id 41},
   :lookup/value :fundraiser},
  :event/name "Tellemann Corporate Party",
...(other fields) 

Notice

• Any direct fields or anything of cardinality 1 had no problem updating.
• but any cardinality/many items either were duplicating or were no being removed from the vector even when I am trying to.
• since some fields change and others do not (like event/contacts) I am confident there transact! is doing its job and must be how I am passing along the data...

Am I doing something wrong or what is the correct map layout to request a ref be removed to a non-component entity ?

Thanks

[tonsky]

With cardinality/many and entity maps in tx, all values mean "add those to the ones you have". In your case,

:event/contacts [{:contact/name "Nina Simone", :db/id 56}],

Means "Add 56 to whatever values you already have". Given that 56 is already in event/contacts, nothing changed.

To explicitly delete, use vector tx:

[:db/retract 61 :event/contacts 56]

There’s not built-in combined add/remove operation for cardinality-many attributes, but you can build one if you want.

[jamesnyika]

Keeping this open till I can verify. Will close as soon as I make it save.. thank you for the update

[jamesnyika]

Confirming that sending a transaction with

[[:db/retract 63 :event/contacts 56]] 

works and does retract that datom 56 for the entity id 63.

Also confirmed if you want to submit multiple retractions just add more vectors with more values like so

[[:db/retract 63 :event/contacts 56][:db/retract 63 :event/contacts 55]] 

This will remove two entities :db/id 55 and :db/id 56 from the cardinality/many called :event/contacts

Thank you @tonsky !! Fantastic work on all this.

A final questions, when can you use Maps and when can you use vectors only ? Is that specified anywhere ?

thanks

[jamesnyika]

I added a note in the FAQ for anyone else looking
Reference it here