CODEWITHSUNDEEP
ooparchitecturerepositorydomain-driven-design
MindFork
MindFork

Reputation: 25

Relations between Repositories for Aggragates in DDD

I'm building a Repository for an Aggragate. We've got 3 different Entities that it's constructed out of, one of them is root.

Data for all 3 is persisted in a SQL database. Each has it's own table.

Let's consider simple case of getting full list of those Aggregates. I need to fetch data from all 3 tables. Should I build one optimised query to fetch this data set or rather encapsulate logic for each Entity in it's own Repository and assemble it the Aggragate's repo? (Aggregate repo would then call respective repos and assemble it)

I'm leaning twords the first solution, however it's stronger coupleing. The later seems nicer from OOP point of view, but seems to be overcomplicated and potentialy casue problems with cache invalidation for subsequent sets of data etc.

Upvotes: 1

Views: 78

Answers (1)

Jonatan Dragon
Jonatan Dragon

Reputation: 4997

For each type of object requiring global access, create an object that provides the illusion of all objects of this type stored in memory. Configure access through the global interface. [..] Define methods for adding and removing objects. [..] Define repositories only for aggregates. ~ Evans, about repositories

You should create one repository for Aggregate only. There is no reason to create seperate repositories. What is more, creating seperate repository would cause some additional problems as you mentioned.

I'm leaning twords the first solution, however it's stronger coupleing.

To answer that, please take a look at Aggregate definition from Martin Fowler:

Aggregate is a pattern in Domain-Driven Design. A DDD aggregate is a cluster of domain objects that can be treated as a single unit. An example may be an order and its line-items, these will be separate objects, but it's useful to treat the order (together with its line items) as a single aggregate.

Aggregate is coupling Entities that it is constructed out of by definition.

Upvotes: 2

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