Domain-Driven Design: Tackling Complexity in the Heart of Software

Cargo
has some meaning even when
considered apart from the 
Cargo
itself. So the 
Handling Event
should be the root of its own
AGGREGATE
.
Figure 7.3. A
GGREGATE
 boundaries imposed on the model. (Note: An
ENTITY
 outside a drawn boundary is implied to be the root of its own
AGGREGATE
.)

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[ Team LiB ]

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[ Team LiB ]
Selecting R
EPOSITORIES
There are five 
ENTITIES
in the design that are roots of 
AGGREGATES
, so we can limit our
consideration to these, since none of the other objects is allowed to have 
REPOSITORIES
.
To decide which of these candidates should actually have a 
REPOSITORY
, we must go back to the
application requirements. In order to take a booking through the 
Booking Application
, the user
needs to select the 
Customer(s)
playing the various roles (shipper, receiver, and so on). So we
need a 
Customer Repository
. We also need to find a 
Location
to specify as the destination for
the 
Cargo
, so we create a 
Location Repository
.
The 
Activity Logging Application
needs to allow the user to look up the 
Carrier Movement
that a 
Cargo
is being loaded onto, so we need a 
Carrier Movement Repository
. This user must
also tell the system which 
Cargo
has been loaded, so we need a 
Cargo Repository
.
Figure 7.4. R
EPOSITORIES
 give access to selected