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Filter Attribute

Filter Attribute

Molecule can filter an attribute by the value of another attribute.

Imagine for instance football players and their goals and assists:

Player.name.goals.assists.insert(
  ("Celso", 1, 2),
  ("Messi", 3, 3),
  ("Salah", 5, 3),
).transact

Equality

Now we can find players who have an equal number of goals and assists

Player.name.goals(Player.assists_).query.get ==> List(("Messi", 3))

Filter attributes (like assists_) should be tacit and without applied operations.

Make the left-hand side attribute goals_ tacit too if you want the player name only

Player.name.goals_(Player.assists_).query.get ==> List("Messi")

Comparison

We can compare two values with various comparators and simply add the filter attribute again as a mandatory attribute to get that value too:

// Different number of goals and assists
Player.name.goals.not(Player.assists_).assists.query.get ==> List(
  ("Celso", 1, 2),
  ("Salah", 5, 4),
)

// Fewer goals than assists
Player.name.goals.<(Player.assists_).assists.query.get ==> List(
  ("Celso", 1, 2),
)

// More goals than assists
Player.name.goals.>(Player.assists_).assists.query.get ==> List(
  ("Salah", 5, 4),
)

// Fewer or equally many goals as assists
Player.name.goals.<=(Player.assists_).assists.query.get ==> List(
  ("Celso", 1, 2),
  ("Messi", 3, 3),
)

// More or equally many goals as assists
Player.name.goals.>=(Player.assists_).assists.query.get ==> List(
  ("Messi", 3, 3),
  ("Salah", 5, 4),
)

1 sub filter

We can further narrow the result by adding a sub filter on the filter attribute

equal
// More or equally many goals than assists when assists == 3
Player.name.goals.>=(Player.assists_)
  .assists(3).query.get ==> List(
  ("Messi", 3, 3),
)

// More or equally many goals than assists when assists == 4
Player.name.goals.>=(Player.assists_)
  .assists(4).query.get ==> List(
  ("Salah", 5, 4),
)

Or we could add a sub filter on the calling attribute goals instead:

// More or equally many goals than assists when goals >= 3
Player.name.goals_.>=(3)
  .goals.>=(Player.assists_).assists.query.get ==> List(
  ("Messi", 3, 3),
  ("Salah", 5, 4),
)

// More or equally many goals than assists when goals >= 4
Player.name.goals_.>=(4)
  .goals.>=(Player.assists_).assists.query.get ==> List(
  ("Salah", 5, 4),
)

2 sub filters

We can add sub filters to both the calling attribute goals and filter attribute assists:

equal
// More or equally many goals than assists
// when goals == 3 and assists >= 3
Player.name.goals_(3)
  .goals.>=(Player.assists_)
  .assists.>=(3).query.get ==> List(
  ("Messi", 3, 3),
)

// More or equally many goals than assists
// when goals == 5 and assists >= 3
Player.name.goals_(5)
  .goals.>=(Player.assists_)
  .assists.>=(3).query.get ==> List(
  ("Salah", 5, 4),
)

Cross ns

So far we have compared attributes of the same entity. We can also compare an attribute with a filter attribute from a related entity. Let's expand our example data a bit by adding a relationship:

Player.name.goals
  .Team.name.goalsToBonus.bonus.query.get ==> List(
  ("Celso", 1, "Champions", 3, 1000000),
  ("Messi", 3, "Champions", 3, 1000000),
  ("Salah", 5, "Galactico", 4, 5000000),
)

Now we can ask questions across related entities like "which players of what teams scored enough goals to get a bonus?"

Player.name.goals.>=(Team.goalsToBonus_)
  .Team.name.goalsToBonus.bonus.query.get ==> List(
  ("Messi", 3, "Champions", 3, 1000000),
  ("Salah", 5, "Galactico", 4, 5000000),
)

Or we can ask the other way around "which teams have players getting a bonus?"

Player.name.goals
  .Team.name.goalsToBonus.<=(Player.goals_).bonus.query.get ==> List(
  ("Messi", 3, "Champions", 3, 1000000),
  ("Salah", 5, "Galactico", 4, 5000000),
)

The attribute in the filter expression has to be tacit, and it has to be present and mandatory in the related entity. Otherwise, Molecule will warn you:

intercept[ModelError] {
  Player.name.goals.>=(Team.goalsToBonus_)
    .Team.name.bonus // goalsToBonus missing
    .query.get
}.msg ==> 
  "Please add missing filter attribute Team.goalsToBonus"

Nested

We can also compare attributes across nested data. If we had for instance instead modelled a Team with a cardinality-many relationship to Players we could a list of teams each with a list of players:

Team.name.goalsToBonus.bonus
  .Players.*(Player.name.goals).query.get ==> List(
  ("Champions", 3, 1000000, List(
    ("Celso", 1),
    ("Messi", 3),
  )),
  ("Galactico", 4, 5000000, List(
    ("Salah", 5),
    ("Yamal", 2),
  )),
)

As before, but now with nested data, we can ask "which players of what teams scored enough goals to get a bonus?"

Team.name.goalsToBonus.<=(Player.goals_).bonus
  .Players.*(Player.name.goals).query.get ==> List(
  ("Champions", 3, 1000000, List(
    ("Messi", 3),
  )),
  ("Galactico", 4, 5000000, List(
    ("Salah", 5),
  )),
)

Or the other way around "which teams have players getting a bonus?"

Team.name.goalsToBonus.bonus
  .Players.*(Player.name.goals.>=(Team.goalsToBonus_))
  .query.get ==> List(
  ("Champions", 3, 1000000, List(
    ("Messi", 3),
  )),
  ("Galactico", 4, 5000000, List(
    ("Salah", 5),
  )),
)

and "which teams have players scoring more goals than goalsToBonus?", and "Champions" is no longer included:

Team.name.goalsToBonus.bonus
  .Players.*(Player.name.goals.>(Team.goalsToBonus_))
  .query.get ==> List(
  ("Galactico", 4, 5000000, List(
    ("Salah", 5),
  )),
)

Filter attributes works the same with optional nested data (using *? instead of *).

Filter attribute compliance tests
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