If a 1:M relationship is mandatory on both sides, which of the following is true?

Question

BlackTom AI · Accepted Answer

Question restatement: If a 1:M relationship is mandatory on both sides, which of the following is true?
Options:
1) Two foreign keys are created as a result of mapping such a relationship, one that can have null (empty values) and one that cannot have null (empty values)
2) The resulting foreign key can have null (empty) values
3) No foreign key is created as a result of mapping such a relationship
4) The resulting foreign key cannot have null (empty) values
5) The resulting foreign key must have null (empty) values

Analysis:
Option 1: This statement claims two foreign keys are created—one nullable and one non-nullable. In a standard 1:N mapping, only one foreign key is created in the many side table to reference the one side. The notion of two FKs with contrasting nullability doesn't align with typical relational design for a single 1:N association. Therefore, this option is incorrect.
Option 2: Saying the resulting foreign key can have null values contradicts the premise that both sides are mandatory. If the many side must reference a valid one-side row, the FK cannot be null. Thus, this option is incorrect.
Option 3: Claiming no foreign key is created is false for a 1:N relationship, where a foreign key from the many side to the one side is the basic mapping mechanism. This option is incorrect.
Option 4: This option states that the resulting foreign key cannot have null values. Given both ends are mandatory, every child in the many-side table must reference an existing parent, enforcing non-null foreign keys. This is correct.
Option 5: The assertion that the foreign key must have null values is incorrect for the same reason as Option 2: mandatory participation forbids nulls in the FK.

Summary: The only option that coherently reflects mandatory participation on both sides of a 1:M relationship is that the foreign key cannot be null, since every child must point to a parent. The other statements misinterpret how foreign keys and nullability operate in a standard 1:N mapping with mandatory constraints.

If a 1:M relationship is mandatory on both sides, which of the following is true?

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