There is a discrepancy between the designed diagram and the generated keys:

• you designed a one-to-many relationship for Wallet with WalletPlatform, WalletStorage and CryptoCurrency (i.e. one wallet could have several platforms, storage or currencies), but
• the foreign keys generated by Hibernate in the Wallet implement a many-to-one in the opposite direction (i.e. a wallet can have only one platform, storage or currency, but those could be associated with several wallets).

Is it possible that you have a mismatch in the Hibernate definition of the associations/relations? In case of doubt, don't hesitate to update your question with the annotations you've used.

Looking further, it appears that there is an error with the relationship between Wallet and CryptoCurrency, in both the designed diagram and the foreign keys:

• according to your diagram, a Wallet can be associated with several CryptoCurrency rows, but each crypto-currency can only be associated to a single wallet. For example, only one wallet could use bitcoins?? Are there really many more currenclies than there are wallets in your system?
• according to the generated FK, a wallet could be associated to a single currency, but a currency could be used by several wallets.

This seems not correct: I understand that a wallet should be able to hold several crypto-currencies, and a crypto-currency can be held by several wallets. That's many-to-many. This is a reality of the domain model and it makes no sense to avoid many-to-many for obscure reasons. The many-to-many association implies the use of an association table, and hibernate is perfectly able to generate it.

Of course, if you really want to avoid many-to-many, you could use an intermediate entity (e.g.CurrencyInWallet), and two one-to-many associations to replace the many-to-many. But what would be the advantage?

The schema is inconsistent

There is a discrepancy between the designed diagram and the foreign keys:

• you designed in your diagram a one-to-many relationship for Wallet with WalletPlatform, WalletStorage and CryptoCurrency (i.e. one wallet could have several platforms, storage or currencies), but
• the foreign keys added in the schema to the Wallet implement a many-to-one in the opposite direction (i.e. a wallet can have only one platform, storage or currency, but those could be associated with several wallets).

Is it possible that you have a mismatch in the Hibernate definition of the associations/relations? In case of doubt, don't hesitate to update your question with the annotations you've used.

And a missing many-to-many relationship?

I’m not very knowledgeable of the wallet world, but I am very familiar with currencies. In this respect, I wonder if the relationship between Wallet and CryptoCurrency, in both the designed diagram and the foreign keys is correct:

• according to your diagram, a Wallet can be associated with several CryptoCurrency rows, but each crypto-currency can only be associated to a single wallet. For example, only one wallet could use bitcoins and all the other wallets have to use something else??
• according to the generated FK, a wallet could be associated to a single currency, but a currency could be used by several wallets.

I understand that a wallet should be able to hold several crypto-currencies, and a crypto-currency can be held by several wallets. That's many-to-many. There is absolutely no valid reason to avoid many-to-many if this is the reality of the domain.

Many-to-many implies the use of an association table (also called junction table, intersect table or bridge table):

• hibernate is perfectly able to generate it (see for example this SO answer).
• if you prefer, you can manually break down the many-to-many in your diagram with two one-to-many relations with an intermediate entity (e.g.CurrencyInWallet).

Hint: The breakdown with an additional entity makes sense if it reveals a well identified domain entity (e.g an “assignment”), and even more if it could have own attributes. But often, this is not the case and the additional entity would seems somewhat artificial; it usually start with the difficulty to find an entity name. In this case, prefer to keep your diagram simple and just use a junction table without promoting it to a full-blown entity

There is a discrepancy between:

• the one-to-many relationship that you designed for Wallet with WalletPlatform, WalletStorage and CryptoCurrency (i.e. one wallet could have several platforms, storage or currencies), and
• the foreign keys generated by Hibernate in the Wallet, which implement a many-to-one in the opposite direction (i.e. a wallet can have only one platform, storage or currency, but those could be associated with several wallets.

Looking further, it appears that there is an inconsistency with the relationship between Wallet and CryptoCurrency, in both the designed diagram and the foreign keys:

• according to your diagram, a Wallet can be associated with several CryptoCurrency rows, but each crypto-currency can only be associated to a single wallet? For example, only one wallet could use bitcoins?? Are there really many more currenclies than there are wallets in your system?
• according to the generated FK, a wallet could be associated to a single currency, but a currency could be used by several wallets.

This is wrong in every possible way: a wallet should be able to hold several crypto-currencies, and a crypto-currency can be held by several wallets. That's many to many. This is a reality of the domain model and it makes no sense to avoid many-to-many for obscure reasons. THe many-to-many association implies the use of an association table, and hibernate is perfectly able to generate it.

There is a discrepancy between the designed diagram and the generated keys:

• you designed a one-to-many relationship for Wallet with WalletPlatform, WalletStorage and CryptoCurrency (i.e. one wallet could have several platforms, storage or currencies), but
• the foreign keys generated by Hibernate in the Wallet implement a many-to-one in the opposite direction (i.e. a wallet can have only one platform, storage or currency, but those could be associated with several wallets).

Is it possible that you have a mismatch in the Hibernate definition of the associations/relations? In case of doubt, don't hesitate to update your question with the annotations you've used.

Looking further, it appears that there is an error with the relationship between Wallet and CryptoCurrency, in both the designed diagram and the foreign keys:

• according to your diagram, a Wallet can be associated with several CryptoCurrency rows, but each crypto-currency can only be associated to a single wallet. For example, only one wallet could use bitcoins?? Are there really many more currenclies than there are wallets in your system?
• according to the generated FK, a wallet could be associated to a single currency, but a currency could be used by several wallets.

This seems not correct: I understand that a wallet should be able to hold several crypto-currencies, and a crypto-currency can be held by several wallets. That's many-to-many. This is a reality of the domain model and it makes no sense to avoid many-to-many for obscure reasons. The many-to-many association implies the use of an association table, and hibernate is perfectly able to generate it.

Of course, if you really want to avoid many-to-many, you could use an intermediate entity (e.g.CurrencyInWallet), and two one-to-many associations to replace the many-to-many. But what would be the advantage?