Regression prevent using update to remove an entry from a map [DATACASS-841]

[spring-projects-issues]

Luc Boutier opened DATACASS-841 and commented

When migrating a project from 2.x to 3.x I encountered an issue on map field remove operation in a map.

@Table("contact")
class Contact(
    @PrimaryKeyColumn(name = "account_key", ordinal = 0, type = PrimaryKeyType.PARTITIONED)
    var accountKey: UUID,
    @PrimaryKeyColumn(name = "id", ordinal = 1, type = PrimaryKeyType.PARTITIONED)
    var id: UUID,
    @Column("entity_details")
    var entityDetails: MutableMap<UUID, ContactEntityDetails> = mutableMapOf()
)

// Later in some update method:
val update = Update.RemoveOp(ColumnName.from("entityDetails"), entityId)
val query = Query.query(
    Criteria.where("accountKey").`is`(accountKey),
    Criteria.where("id").`is`(id)
)
return cassandraTemplate.update(query, update, Contact::class.java)

 

The update statement generated is the following:

UPDATE contact SET entity_details=entity_details-00000000-0000-4000-9000-000000000002 WHERE account_key=f9b520c9-c928-4360-ae69-90d4373cbd57 AND id=6dd405dc-cfbb-40ec-a626-ec18df63ab6d

There is curly braces missing as stated here 

 And this should be if I'm correct

UPDATE contact SET entity_details=entity_details-{00000000-0000-4000-9000-000000000002} WHERE account_key=f9b520c9-c928-4360-ae69-90d4373cbd57 AND id=6dd405dc-cfbb-40ec-a626-ec18df63ab6d

 

 

---

Affects: 3.1.2 (2020.0.2)

[mp911de]

Hey @lucboutier, there are a couple of issues here. We didn't expose remove from map as we missed that one. Map value removal is limited to a single element only because the DataStax QueryBuilder API. Let's see whether we can navigate around that limitation.

Deleting map entries works only by specifying the value, not the key. For whatever reason, CQL requires a DELETE statement to remove a map entry by key.

[mp911de]

That's interesting. entity_details=entity_details-{'hello'} removes the entry by key, not by value. What's a bit strange is that Assignment.removeMapEntry(…) expects a key and a value (both non-null) and the implementation checks only if the key is non-null which can easily lead to the assumption that map removals happen by value.

The docs meanwhile aren't fully clear and a bit confusing:

Alternatively, remove all elements having a particular value using the UPDATE command, the subtraction operator (-), and the map key values in curly brackets.

It should be:

Alternatively, remove all elements having a particular key using the UPDATE command, the subtraction operator (-), and the map key values in curly brackets.

/cc @adutra

[mp911de]

This change requires quite some changes, so backporting it only to 3.1.x and master.

[lucboutier]

Indeed I got confused by our workaround implementation and past behavior when reading your initial comment and actual documentation again.. That's indeed weird..

Note that our current workaround is to use a prepared statement that we create through the following:

         stmtCache, QueryBuilder.update("contact")
             .remove("entity_details", QueryBuilder.bindMarker("entity_id"))
             .whereColumn("account_key").isEqualTo(QueryBuilder.bindMarker("account_key"))
             .whereColumn("id").isEqualTo(QueryBuilder.bindMarker("id"))
             .ifExists()
             .build()
     ).createPreparedStatement(session)```