I have three entities :
Technician
Vehicle
Repair
The question is how to model this in ERD? Knowing that a technician can repair multiple cars, and the same car can be repaired by one and only one technician? How should the repair entity tied to all this?
2
You need to specify more description of your tables and of your requirements. Anyway, here is one way to model the tables. However, in a real application there would be other things to consider. Only PKs and FKs are shown. Other columns depend on your case.
Note:
In the original version of the answer, I missed the requirement that “the same car can be repaired by one and only one technician”. To implement this, in the Repair_Job table, the TechID column + VIN column should be constrained to be unique.
2
CONCEPTUAL
Note that in the ERD ( conceptual data model ) you don’t specify the foreign keys, they are implicit in the relationship ( lines ).
Your data modeling tool will generate the foreing keys for you when you generate the physical data model (RDBMS dependant):
PHYSICAL