I'm dealing with a legacy database that uses a strange key/ID configuration for one of its tables. It's the table that defines user information. Here are the columns (I've simplified things a little):
ID
Secondary ID
First Name
Last Name
Change Type
All of these columns are part of the key in the database itself and are needed to uniquely identify a row, with one exception. When the Change Type column has a null value then the ID column uniquely identifies a row. This exception is heavily relied on to get a user's name based on their ID. However I need to specify all columns as #Id for hibernate to work correctly with this table ... or do I? Assuming I do, how would I go about also implementing the exception so that objects can be loaded from the database by just the ID? Ideally I'd like to be able to interact with this object as if ID was the only key since in practice that's how it's done in straight SQL by the DBAs.
Related
I am running a Spring Boot application were I use JPA. I am using Postgresql as DB.
I get some data from an api where there is no Id for each row. So I have to use #Id and #GeneratedValue. But my problem is that when I request this data again I might get the exact same rows or some of them again. I can make a composite key that consist of 3 of the columns but then how do I do with the Id that I would like to keep (autogenerated value). If I understand correct, I can´t use composite primary key and a generate #Id at the same time?
An extension of this question is that sometimes a column in each row are updated. Then I would like to update only this column and not create a new row in the DB.
I could make a modified query that checks if the three column (composite key) already exist then I update that row if any change or if row is missing just save. Or is their any other option that I have missed so I do not have to write any query myself?
You are correct, you have to decide if you want to use a single autogenerated Id or a composite key, you can't have both at the same time. And if your API can't handle a single Id you are probably better of doing as you are thinking in your extended question; creating a composite key and when updating rows check for a row that match your three values.
I am trying to track changes made to a database (schema) using a java app. We are trying to track changes for each column/unique-constraint/index and table.
Functionally I know table.column is unique. So, if the datatype of a column changes, we know which column to find and record the change. But what if the name changes? If JDBC's result set is ordered (it asks for index), then I can rely on the order to give me the same column everytime, even if the name changes. Will there be any surprises here, since it is a result 'set'?
However, I learnt that we can change the order of the columns as well. Isn't there any unique ID associated with the columns so that they can be picked up on that basis?
I would mostly not want to use information_schema route, but even though i checked there for mysql, found nothing useful.
I have the following table in my db:
CREATE TABLE document (
id INT PRIMARY KEY AUTOINCREMENT,
productModelId INT NOT NULL,
comment VARCHAR(50),
CONSTRAINT FK_product_model FOREIGN KEY (productModelId) REFERENCES product_model(id),
)
Of course, real table is much more complicated, but this is enough to understand the problem.
Our users want to see the number of the document when they click button "new". So, in order to do that, we have to create object in db and send to client that object. But, there is a problem. We need to know productModelId before we save the object in db. Otherwise we will have an sql exception.
I see two possible variants (both are ugly, really):
To show modal list with product models to user and after that create object in database with productModelId chosen by user.
To create a temporary number and after that to save the object in db when user finishes editing the document and saves id. We also need to remove NOT NULL case and validate this somwhere in code.
The first way is bad because we have too much modals in our application. Our UI is too heavy with them.
The second variant is ugly because our database is not consistent without all the checks.
What can you suggest we do? Any new solutions? What do you do in your apps? May be some UI tips. We are using the first variant at the moment.
Theory says that the id you use on your database should not be a relevant information, so the user should not see it if not well hidden in an URL or similar, so you should not display it to the user, and the problem you have is one possible confirmation of this theory.
Right now the solution you have is partially correct: it satisfies technical requirements, but is still bad because if the user doesn't complete the insert you'll end up with the DB having empty records (meaning, with ID and foreign key ok, but all other fields empty or with useless default values), so you are basically circumventing the database validations.
There are two better solutions, but both require you to review your database.
The first is not to use the id as something to display to the user. Use another column, with another "id", declare it unique on the database, generate it at application, display it to the user, and then use this other "id" (if it's unique, it is effectively an id) wherever needed.
The second one is the one that is being used often cause it does not require a central database or other authority to check uniqueness of ids, so scales better in distributed environments.
Drop the use of the common "id int" auto-incremented or not, and use UUIDs. Your id will be a varchar or a binary, an UUID implementation (like java.util.UUID, but you can find in other languages) will generate a unique id by itself whenever (and wherever, even on the client for example) you need it, and then you supply this id when saving.
We make it the following way.
Created table id_requests with fields issue_type_id and lastId. We need this in order to avoid the situation when two users hit the button 'new' and get the same ids.
And of course we added field innerNum to all the tables we use this feature in.
Thank you!
I have a SQL Server database that holds a table where a varchar column has a check constraints on it to make sure only a few different words can be entered as a value (names).
Like this
CONSTRAINT chk_Names CHECK (name IN ('John', 'Eva', 'Carl', 'Fred'))
What I want do do is to populate a combobox in java with these names, and I don't want to manually enter them since they might change in the database. I want to populate it from metadata.
But I haven't been able to find a way to get the information from the database either with the INFORMATION_SCHEMA or sys.objects (or from DatabaseMetaData in java for that matter)
I'm quite new to SQL Server but is it possible to get that information somehow?
Regards
/Fred
It sounds like you should move the list of names to a table. You're Java form could select the data from the table.
And, because the data can change, it will be better to update the table than to change the check constraint. You can change the check constraint to a foreign key constraint too.
You can also find the check-constraint definitions in INFORMATION_SCHEMA.CHECK_CONSTRAINTS. The expression is in the CHECK_CLAUSE column; and, you'll have to extract the values from the expression.
I'm currently using ORMLite to work with a SQLite database on Android. As part of this I am downloading a bunch of data from a backend server and I'd like to have this data added to the SQLite database in the exact same format it is on the backend server (ie the IDs are the same, etc).
So, my question to you is if I populate my database entry object (we'll call it Equipment), including Equipment's generatedId/primary key field via setId(), and I then run a DAO.create() with that Equipment entry will that ID be saved correctly? I tried it this way and it seems to me that this was not the case. If that is the case I will try again and look for other problems, but with the first few passes over the code I was not able to find one. So essentially, if I call DAO.create() on a database object with an ID set will that ID be sent to the database and if it is not, how can I insert a row with a primary key value already filled out?
Thanks!
#Femi is correct that an object can either be a generated-id or an id, but not both. The issue is more than how ORMLite stores the object but it also has to match the schema that the database was generated with.
ORMLite supports a allowGeneratedIdInsert=true option to #DatabaseField annotation that allows this behavior. This is not supported by some database types (Derby for example) but works under Android/SQLite.
For posterity, you can also create 2 objects that share the same table -- one with a generated-id and one without. Then you can insert using the generated-id Dao to get that behavior and the other Dao to take the id value set by the caller. Here's another answer talking about that. The issue for you sounds like that this will create a lot of of extra DAOs.
The only other solution is to not use the id for your purposes. Let the database generate the id and then have an additional field that you use that is set externally for your purposes. Forcing the database-id in certain circumstances seems to me to be a bad pattern.
From http://ormlite.com/docs/generated-id:
Boolean whether the field is an auto-generated id field. Default is false. Only one field can have this set in a class. This tells the database to auto-generate a corresponding id for every row inserted. When an object with a generated-id is created using the Dao.create() method, the database will generate an id for the row which will be returned and set in the object by the create method. Some databases require sequences for generated ids in which case the sequence name will be auto-generated. To specify the name of the sequence use generatedIdSequence. Only one of this, id, and generatedIdSequence can be specified.
You must use either generatedId (in which case it appears all ids must be generated) or id (in which case you can set them) but not both.