9 Advanced entity association mappings
This chapter covers
- Applying mapping through one-to-one entity associations
- Using one-to-many mapping options
- Creating many-to-many and ternary entity relationships
In the previous chapter, we demonstrated a unidirectional many-to-one association, made it bidirectional, and finally enabled transitive state changes with cascading options. One reason we discuss more advanced entity mappings in a separate chapter is that we consider quite a few of them rare or at least optional. It’s possible to only use component mappings and many-to-one (occasionally one-to-one) entity associations. You can write a sophisticated application without ever mapping a collection! We’ve demonstrated the particular benefits to gain from collection mappings in the previous chapter; the rules for when a collection mapping is appropriate also apply to all examples in this chapter. Always make sure you actually need a collection before attempting a complex collection mapping.
Let’s start with mappings that don’t involve collections: one-to-one entity associations.