¿Debería estar expuesto una clave sustituta a un usuario?

Question

A menudo en una tabla que no tiene una clave natural, todavía es útil para que los usuarios puedan tener un identificador generado de forma única.Si la tabla tiene una clave principal sustituta (y en tal caso, sin duda, lo esperará) si esa clave estuviera expuesta al usuario o si se usara otro campo para ese propósito?

Una razón para no exponer la clave sustituta es que ahora no puede hacer operaciones que conserven la relación entre los registros, pero cambie los valores clave, como ciertos tipos de eliminación / reinserción, muchos métodos de copia de datos deuna base de datos a otra, etc.

La principal ventaja de exponer la clave sustituta es la simplicidad de usar un campo que tiene de todos modos.

En ¿Qué circunstancias es mejor exponer directamente a la clave sustituta a los usuarios?

Answer 1

Debe estar listo para cualquier identificador que esté expuesto a los usuarios / clientes que necesiten ser cambiados, y cambiar la identidad de una fila en una base de datos y propagarse de que el cambio a todas las claves externas está solicitando a romper los datos.

Si los datos no tienen una clave de negocio natural, puede agregar un campo adicional para un "identificador de negocios". Esto debe optimizarse para los procesos en los que se utiliza. La entrada del teclado de teléfono significa solo numérico. Sobre el teléfono / medios verbales Evite símbolos de sondeo similares (B / D, M / N, etc.). Incluso puede autodogenear una frase fácilmente memorable ("jalea verde").

El efecto de esto es que la empresa puede cambiar más adelante cómo quieren referirse a los registros, y el único cambio de esquema de datos agrega una nueva columna para ese estilo de identificación o transformar los IDS que ya están allí. El cambio no se propaga a través de toda la base de datos, y aún tiene una identificación (el sustituto) que es válido con el tiempo.

En resumen, evitaría exponer las claves de sustitutas a los usuarios. Como señalan los comentarios, las claves sustitutas casi nunca deben cambiar. A la inversa, las empresas quieren cambiar todo. Si la clave sustituta está expuesta, es solo cuestión de tiempo antes de que el negocio quiera cambiarlo.

Como nota lateral, cuando digo "exponer" aquí, quiero decir para darle la clave al usuario con la expectativa de que usan directamente (como llamar a su número de pedido ).

Answer 2

In some cases, surrogate keys are expected and make sense to users. My favorite example is "order number". Order number isn't really a natural key: a natural key might be timestamp plus user, or maybe more than that if you expect users to generate more than one order within the granularity of your timestamp.

Nonetheless, users understand and expect the convenience of an order number. There is no harm, and lots of value, if you let users know about them.

On the other hand, some surrogate keys make no sense to a user. Sure, my health insurance company has some surrogate key that identifies me based on my member id, date of birth, carrier, etc, but I don't care about that, I care about the info on my card (which often includes ids based on my employer and are not unique across the universe... Hence the surrogate key at the insurance company).

Answer 3

In layman's words:

• Surrogates should be hidden from the user.
• You should expose some other business candidate key to the user.
• If no other candidate key exist you should show the PK. But in this case the PK is not considered a surrogate since it's not a substitute for other column.

Answer 4

you should ONLY expose a field to a user that provides useful information to the user, either directly or in reporting defects to you.

conversely, you should ALWAYS expose "surrogate primary keys" when they are the principal means of identifying a record (simple or complex) for an interaction the user performs.

Answer 5

You should only expose a surrogate key if it's a properly generated GUID/UUID*. Exposing sequential surrogate keys is number 4 on the OWASP Top 10 security issues.

* In practice, it's best to assume that it wasn't properly generated for these purposes unless you know that it was created by a cryptographically secure random or pseudo-random number generator.

Answer 6

If a table has no natural key, surrogate keys allow rows like this.

surrogate_key  some_name
--
1              Wibble
2              Wibble
...
17             Wibble
...
235            Wibble

I'd call these artificial keys instead of surrogate keys, but that distinction isn't important for this question.

Now, assuming that there's important data referencing these surrogate keys through foreign keys, how would the end users know which row to update if they don't know the surrogate key values?

Answer 7

It shouldn't matter whether you expose the keys or not to the end user. Your application should perform the necessary authorization such that simply knowing an order id, for example, can't allow them access to something they normally wouldn't have access to.

caveat: this assumes a web based or n-tier application where server side authorization is possible/feasable. If you have a VB app thats directly executing sql, thats a whole 'nother issue.

Answer 8

According to the principle of encapsulation, which is a foundational concept in OOP, you should hide implementation details. Once a surrogate becomes public it becomes data. One man's surrogate key is the next man's natural key.

In practice I think surrogate keys should be encapsulated at the boundary of a service layer. If you have a service for some aggregate root then the internal domain objects and repository would all use the surrogate key. These internals would all be encapsulated. The public API would use some other format which could include nesting to hide parent keys, so hiding the surrogate key of the root record isn't exactly a seven year leap.

Answer 9

One health-care company that I did a project for had a nasty problem with their "provider IDs." These were originally hand-managed and they contained embedded information. A single provider might have more than one ID, and had to know the "right" one to use at each clinic. And, unfortunately, some provider-IDs had been assigned to more than one provider at a time!

To solve the problem and to allow several different systems to communicate with each other unambiguously, I created an internal-only system of surrogate keys: they were simply random strings of letters that were the same length as the old (numeric) provider-ID strings. This was done so that column-sizes and data types didn't have to be changed.

One master system had to take a provider-ID, "figure out who it meant," and return the proper surrogate key, which always corresponded 1:1 to a single person.

Sometimes, that same system had to go the other way ... "which (legacy) provider-ID should we give them when referring to [this_person_surrogate] in [that_system]?"

Each of the downstream systems was now re-coded to use these unambiguous surrogate keys to refer to persons, knowing that every other system would be using only the same surrogate value.

Within each system's database, auto-increment integers were conveniently used as primary and foreign keys, and these keys were of course never shared with any other system. The record for each "person" contained its surrogate.

Any request that one system made to another system always used the surrogate. No system ever knew what any other system's "primary keys" were.

Carrying this concept one step further, surrogate keys were never published externally. The company eventually re-vamped its provider-ID system in an effort to clean up their mess, but when they did so we created a new provider-id "for public consumption," and tied those values to the surrogates just as we had done with the old IDs. Thus, the "purity" of the surrogates was not compromised, and the company didn't have to give its providers "ugly character strings."