DDD - the rule that Entities can't access Repositories directly

Question

In Domain Driven Design, there seems to be lots of agreement that Entities should not access Repositories directly.

Did this come from Eric Evans Domain Driven Desi

Answer 1

To cite Carolina Lilientahl, "Patterns should prevent cycles" https://www.youtube.com/watch?v=eJjadzMRQAk, where she refers to cyclic dependencies between classes. In case of repositories inside aggregates, there is a temptation to create cyclic dependencies out of conveniance of object navigation as the only reason. The pattern mentioned above by prograhammer, that was recommended by Vernon Vaughn, where other aggregates are referenced by ids instead of root instances, (is there a name for this pattern?) suggests an alternative that might guide into other solutions.

Example of cyclic dependency between classes (confession):

(Time0): Two classes, Sample and Well, refer to each other (cyclic dependency). Well refers to Sample, and Sample refers back to Well, out of convenience (sometimes looping samples, sometimes looping all wells in a plate). I couldn't imagine cases where Sample would not reference back to the Well where it's placed.

(Time1): A year later, many use cases are implemented .... and there are now cases where Sample should not reference back to the Well it's placed in. There are temporary plates within a working step. Here a well refers to a sample, which in turn refers to a well on another plate. Because of this, weird behaviour sometimes occurs when somebody tries to implement new features. Takes time to penetrate.

I also was helped by this article mentioned above about negative aspects of lazy loading.