Feature request - Support for filtering specific schemas for collection filter

[ereb2impact]

Hi,

An example of filtering specific schema could be:

from decimal import Decimal
import dataframely as dy
import polars as pl

class InvoiceIdSchema(dy.Schema):
    invoice_id = dy.String(primary_key=True)

class InvoiceSchema(InvoiceIdSchema):
    admission_date = dy.Date(nullable=False)
    discharge_date = dy.Date(nullable=False)
    received_at = dy.Datetime(nullable=False)
    amount = dy.Decimal(nullable=False, min_exclusive=Decimal(0))

    @dy.rule()
    def discharge_after_admission(cls) -> pl.Expr:
        return pl.col("discharge_date") >= pl.col("admission_date")

    @dy.rule()
    def received_at_after_discharge(cls) -> pl.Expr:
        return pl.col("received_at").dt.date() >= pl.col("discharge_date")

class DiagnosisSchema(InvoiceIdSchema):
    diagnosis_code = dy.String(primary_key=True, regex=r"[A-Z][0-9]{2,4}")
    diagnosis_date = dy.Date(nullable=False)
    is_main = dy.Bool(nullable=False)

    @dy.rule(group_by=["invoice_id"])
    def exactly_one_main_diagnosis(cls) -> pl.Expr:
        return pl.col("is_main").sum() == 1

class HospitalClaims(dy.Collection):
    invoices: dy.LazyFrame[InvoiceSchema]
    diagnoses: dy.LazyFrame[DiagnosisSchema]

    @dy.filter(members=["diagnoses"])  # Apply filter only to diagnoses member
    def diagnosis_date_after_admission(self) -> pl.LazyFrame:
        """
        Filter diagnoses to only include those where diagnosis_date >= admission_date.
        This requires joining with invoices to get admission_date.
        
        Returns: LazyFrame with valid diagnoses rows
        """
        return self.diagnoses.join(
            self.invoices.select(["invoice_id", "admission_date"]),
            on="invoice_id",
            how="left"
        ).filter(
            pl.col("diagnosis_date") >= pl.col("admission_date")
        )

    @dy.rule()  # Collection-level validation across members
    def diagnosis_before_discharge(self) -> pl.LazyFrame:
        """
        Validate that all diagnosis dates occur before or on discharge date.
        
        Returns: LazyFrame with rows that violate this rule (diagnosis_date > discharge_date)
        """
        invalid_rows = self.diagnoses.join(
            self.invoices.select(["invoice_id", "discharge_date"]),
            on="invoice_id",
            how="inner"
        ).filter(
            pl.col("diagnosis_date") > pl.col("discharge_date")
        )
        
        return invalid_rows

Ability to filter only specifc schema for filtering collection.

[AndreasAlbertQC]

Thanks for reaching out @ereb2impact ! We currently only support member-based filtering if you define the filtering in the member schemas themselves. Necessarily, that won't work for your example because you are using multiple members as the same time in order to determine how to filter one specific member. Your use case seems reasonable to me and I can't immediately think of anything we would break with this suggestion