CREATE TABLE journey (
    ...
    bound  VARCHAR(8)  NOT NULL,
    PRIMARY KEY (criteria_id, bound),
    CHECK (bound IN ('OUTBOUND', 'INBOUND'))
);

class Search(
    val id: UUID,
    val criteria: Criteria,

    // selection, trains, ...
)

data class Criteria(
    val tripType: TripType,
    val directTrainOnly: Boolean,
    // journeys...
)

CREATE TABLE search (
      id			CHAR(36)     PRIMARY KEY,
      criteria_id	CHAR(36)	 NOT NULL UNIQUE REFERENCES criteria(id),
      selection_id	CHAR(36)	 REFERENCES selection(id),
      -- ...
  );

CREATE TABLE criteria (
    id          	   CHAR(36)     PRIMARY KEY,
    trip_type          VARCHAR(16)  NOT NULL,
    direct_train_only  BOOLEAN      NOT NULL,
    CHECK (trip_type IN ('ONE_WAY', 'ROUND_TRIP'))
);

class Search(
    val id: UUID,
    val criteria: Criteria,
)

data class Criteria(
    val tripType: TripType,
    val directTrainOnly: Boolean,
)

@Table(name = "criteria")
data class Criteria(
    val tripType: TripType,
    val directTrainOnly: Boolean,
)

@Entity
@Table(name = "search")
data class Search(
    @Id
    val id: UUID,

    @OneToOne
    @JoinColumn(name = "criteria_id")
    val criteria: Criteria,
)

@Entity
@Table(name = "search")
data class Search(
    @Id
    val id: UUID,

    @OneToOne
    @JoinColumn(name = "criteria_id")
    val criteria: Criteria,
)

@Entity
@Table(name = "criteria")
data class Criteria(
	@Id
    val id: UUID,
   
    val tripType: TripType,
    val directTrainOnly: Boolean,
)

@Entity
@Table(name = "search")
data class Search(
    @Id
    val id: UUID,

    @OneToOne
    @JoinColumn(name = "criteria_id")
    val criteria: Criteria,
)

@Entity
@Table(name = "criteria")
data class Criteria(
	@Id
    val id: UUID,
   
    val tripType: TripType,
    val directTrainOnly: Boolean,
)

GET /searches/{id}/criteria/{criteriaId}

@Entity
@Table(name = "criteria")
data class Criteria(
	@Id
    @JsonProperty("criteria_id")
    val id: UUID,
   
    @JsonProperty("tripType")
    val tripType: TripType,
    @JsonProperty("directTrainOnly")
    val directTrainOnly: Boolean,
)

@Entity
@Table(name = "search")
data class Search(
    @Id
    @JsonProperty("id")
    val id: UUID,

    @OneToOne
    @JoinColumn(name = "criteria_id")
    val criteria: Criteria,
)

"journeys": [ ... ],
"trains": [
  { 
    "number": "A", 
    "bound" : "OUTBOUND" 
  },
  { 
    "number": "B", 
    "bound" : "OUTBOUND" 
  }
],
"selection": {
  "OUTBOUND": { "trainNumber": "A" }
}

"legs": [ ... ],
"trains": [
  { 
    "number": "A",
    "bound": "OUTBOUND",
    "selected": true 
  },
  { 
    "number": "B",
    "bound": "OUTBOUND",
    "selected": false 
  },
]

"journeys": [ ... ],
"trains": [
  { 
    "number": "A", 
    "bound" : "OUTBOUND" 
  },
  { 
    "number": "B", 
    "bound" : "OUTBOUND" 
  }
],
"selection": {
  "OUTBOUND": { "trainNumber": "A" }
}

"legs": [ ... ],
"trains": [
  { 
    "number": "A",
    "bound": "OUTBOUND",
    "selected": true 
  },
  { 
    "number": "B",
    "bound": "OUTBOUND",
    "selected": true 
  },
]

"journeys": [ ... ],
"trains": [
  { 
    "number": "A", 
    "bound" : "OUTBOUND" 
  },
  { 
    "number": "B", 
    "bound" : "OUTBOUND" 
  }
],
"selection": {
  "OUTBOUND": { "trainNumber": "A" }
}

"journeys": [ ... ],
"trains": [
  { 
    "number": "A", 
    "bound" : "OUTBOUND" 
  },
  { 
    "number": "B", 
    "bound" : "OUTBOUND" 
  }
],
"selection": {
  "OUTBOUND": { "trainNumber": "A" }
}

@Entity
@Table(name = "criteria")
data class Criteria(
	@Id
    @JsonProperty("criteria_id")
    val id: UUID,
   
    @JsonProperty("tripType")
    val tripType: TripType,
    @JsonProperty("directTrainOnly")
    val directTrainOnly: Boolean,
)

@Entity
@Table(name = "search")
data class Search(
    @Id
    @JsonProperty("id")
    val id: UUID,

    @OneToOne
    @JoinColumn(name = "criteria_id")
    val criteria: Criteria,
)

@Entity
@Table(name = "criteria")
data class Criteria(
	@Id
    @JsonProperty("criteria_id")
    val id: UUID,
   
    @JsonProperty("tripType")
    val tripType: TripType,
    @JsonProperty("directTrainOnly")
    val directTrainOnly: Boolean,
)

@Entity
  @Table(name = "criteria")
  @JsonIgnoreProperties(ignoreUnknown = true)
  @JsonInclude(JsonInclude.Include.NON_NULL)
  data class Criteria(
      @Id
      @GeneratedValue(strategy = GenerationType.UUID)
      @JsonProperty("criteriaId") // ← now the id ships on the wire too
      val id: UUID,

      @Enumerated(EnumType.STRING)
      @JsonProperty("tripType")
      val tripType: TripType,

      @JsonProperty("directTrainOnly")
      val directTrainOnly: Boolean,
)

data class Train(
    val number: String,
    val schedule: Schedule,
    // ...
)

data class Schedule(
    val departure: OffsetDateTime,
    val arrival: OffsetDateTime
) {
    init {
        require(arrival.isAfter(departure)) {
            "arrival cannot precede the departure"
        }
    }
}

CREATE TABLE train (
    ...
    departure CHAR(25) NOT NULL,  -- '2026-10-25T02:30:00+02:00'
    arrival   CHAR(25) NOT NULL,  -- '2026-10-25T02:45:00+01:00'
    CHECK (arrival > departure)   -- looks fine
);

INSERT INTO train (..., departure, arrival, ...) VALUES (
    ...,
    '2026-10-25T02:30:00+02:00',  -- before rollback (CEST)
    '2026-10-25T02:30:00+01:00',  -- after rollback (CET)
    ...
);
-- ERROR: new row violates check constraint

CREATE TABLE search (
      id			CHAR(36)     PRIMARY KEY,
      criteria_id	CHAR(36)	 NOT NULL UNIQUE REFERENCES criteria(id) ON DELETE CASCADE,
      selection_id	CHAR(36)	 REFERENCES selection(id),
      -- ...
  );

CREATE TABLE criteria (
    id          	   CHAR(36)     PRIMARY KEY,
    trip_type          VARCHAR(16)  NOT NULL,
    direct_train_only  BOOLEAN      NOT NULL,
    CHECK (trip_type IN ('ONE_WAY', 'ROUND_TRIP'))
);