A partitioning key is the component of a Cassandra primary key that determines where a row is stored. Cassandra hashes each row’s partition key to determine the partition or partitions managing it. A clustering key, when present, instead controls row ordering within that partition. section 4.1.2
When mapping a domain type with Spring Data Cassandra:
- Annotate the partitioning property with @PrimaryKeyColumn(type = PrimaryKeyType.PARTITIONED). section 4.1.3
- Use another @PrimaryKeyColumn with PrimaryKeyType.CLUSTERED when rows need ordering within the partition. section 4.1.3
- Model Cassandra tables around read operations, often duplicating related data instead of relying on relational-style joins. section 4.1.2
Taco persistence
A Taco mapping uses a UUID id annotated with @PrimaryKeyColumn(type = PrimaryKeyType.PARTITIONED). That id determines the Cassandra partition for each taco row. The createdAt property is mapped as a clustered primary-key column and ordered descending, so newer tacos appear first within a partition. section 4.1.3
Listing 4.1 Annotating the Taco class for Cassandra persistence
package tacos;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.UUID;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
import org.springframework.data.cassandra.core.cql.Ordering;
import org.springframework.data.cassandra.core.cql.PrimaryKeyType;
import org.springframework.data.cassandra.core.mapping.Column;
import org.springframework.data.cassandra.core.mapping.PrimaryKeyColumn;
import org.springframework.data.cassandra.core.mapping.Table;
import com.datastax.oss.driver.api.core.uuid.Uuids;
import lombok.Data;
@Data
@Table("tacos") #1
public class Taco {
@PrimaryKeyColumn(type=PrimaryKeyType.PARTITIONED) #2
private UUID id = Uuids.timeBased();
@NotNull
@Size(min = 5, message = "Name must be at least 5 characters long")
private String name;
@PrimaryKeyColumn(type=PrimaryKeyType.CLUSTERED, #3
ordering=Ordering.DESCENDING)
private Date createdAt = new Date();
@Size(min=1, message="You must choose at least 1 ingredient")
@Column("ingredients") #4
private List<IngredientUDT> ingredients = new ArrayList<>();
public void addIngredient(Ingredient ingredient) {
this.ingredients.add(TacoUDRUtils.toIngredientUDT(ingredient));
}
}
Inspect the complete Taco entity mapping to see the partitioning annotation alongside the table and clustering-key configuration. section 4.1.3
