I now writing automation program for system based on MSSQL Server, using Ruby 1.9.3 and ActiveRecord 3.1.6 without Rails.
Tables have nonstandard ids (stk_id, urb_id, instead of id), also some tables haven't primary keys.
Before I added column id and set it as primary key my program worked very slowly. I waited nearly 3 minutes while the program makes two operations of selection and some little processing in table with 9000 records. But when I added column id and set it as primary key, these operations were finished in less then 10 secs.
Yet another problem I found in deletion operation: it doesn't work at all without primary key in table. Error when trying to delete without primary key:
undefined method `to_sym' for nil:NilClass
I can't modify the table structure of the production database. Maybe someone knows how to solve this problem without adding id columns and setting primary keys?
Remark: A database without primary keys is BAD !
http://www.helium.com/items/1539899-why-a-relational-database-needs-a-primary-key
Using nonstandard keys is no problem, just use self.primary_key = "stk_id"
You may also use composite_primary_keys:
https://github.com/drnic/composite_primary_keys
Create indexed views on each of the tables with no primary key. A unique clustered index as well as other indexes as needed can be applied. Including a single table in the view should prevent you from violating the many conditions an indexed view requires/prohibits.
I suggest looking into using Sequel instead of ActiveRecord. It is not opinionated about the database schema like ActiveRecord is and may be easier to use with a database schema you can't modify.
Related
I have an ASP.NET Core application that uses EF6 for dealing with a third-party application's database.
Everything is working as expected, but I'm unable to insert rows into a joining table.
I have two tables, Users and Groups, and a joining table GroupUser that identifies which users are members of which groups. Users has a PK of UserId, and Groups has a PK of GroupId.
GroupUser has only 3 columns: GroupId, UserId and another column (which is irrelevant for this post). The two foreign keys in this table identify a unique record.
Every time I try to insert into GroupUser, I get the inner exception
The table/view does not have a primary key defined. The entity is read-only
The error is correct. There is no PK, but both of the FKs are marked as keys in the model. Shouldn't VS be able to use those as a PK somehow?
The inserts used to work as some point, but required some manual modification of the .edmx file as XML in order to work. Unfortunately, our version control records containing this modification have been lost (and I wasn't the one originally working on this).
I've looked at and tried about a dozen articles around this, but they generally have to do with views instead of tables, so don't seem applicable to my case. The ones that did seem applicable didn't solve the issue.
The only other clue I have for a solution is this comment I found in the code:
// Important note: If you have updated the edmx file in the [redacted]
// project and suddenly start having problems, the edmx file may need to be
// edited as an xml file so that you can make changes necessary to make
// VS believe that the GroupUser table has a primary key. See revision #[redacted]
I'm able to insert into User and Group tables just fine, and as I've said, I don't have access to the revision log mentioned.
Edit: The database is for a third-party application, and unfortunately, it's not as simple as just modifying the table to add a PK. I wish it was. Problem would be solved. But I've been advised by the vendor not to make this change, as it may have unexpected consequences, and would void our support.
How can I 'trick' EF into thinking the table has a key? I'm also open to other workarounds. Modifying the DB structure is currently out of the question.
I'm updating a table that was originally poorly designed. The table currently has a primary key that is the name of the vendor. This serves as a foreign key to many other tables. This has led to issues with the Vendor name initially being entered incorrectly or with typos that need to be fixed. Since it's the foreign key to relationships, this is more complicated than it's worth.
Current Schema:
Vendor_name(pk) Vendor_contact comments
Desired Schema:
id(pk) Vendor_name Vendor_contact comments
I want to update the primary key to be an auto-generated numeric key. The vendor name field needs to persist but no longer be the key. I'll also need to update the value of the foreign key on other tables and on join tables.
Is the best way to do this to create a new numeric id column on my Vendor table, crosswalk the id to vendor names and add a new foreign key with the new id as the foreign key, drop the foreign key of vendor name on those tables (per this post), and then somehow mark the id as the primary key and unmark the vendor name?
Or is there a more streamlined way of doing this that isn't so broken out?
It's important to note that only 5 users can access this table so I can easily shut them out for a period of time while these updates are made - that's not an issue.
I'm working with SQLDeveloper and Python/Django.
The biggest problem you have is all the application code which references VENDOR_NAME in the dependent tables. Not just using it to join to the parent table, but also relying on it to display the name without joining to VENDOR.
So, although having a natural key as a foreign key is a PITN, changing this situation is likely to generate a whole lot of work, with a marginal overall benefit. Be sure to get buy-in from all the stakeholders before starting out.
The way I would approach it is this:
Do a really thorough impact analysis
Ensure you have complete regression tests for all the functions which rely on the Vendor data
Create VENDOR_ID as a unique key on VENDOR
Add VENDOR_ID to all the dependent tables
Create a second foreign on all the dependent tables referencing VENDOR_ID
Ensure that the VENDOR_ID is populated whenever the VENDOR_NAME is.
That last point can be tackled by either fix the insert and update statements on the dependent tables, or with triggers. Which approach you take will determine on your application design and also the number of tables involved. Obviously you want to avoid the performance hit of all those triggers if you can.
At this point you have an infrastructure which will support the new primary key but which still uses the old one. Why would you want to do this? Because you could go into Production like this without changing the application code. It gives you the option to move the application code to use VENDOR_ID across a broader time frame. Obviously, if developers have been keen on coding SELECT * FROM you will have issues that need addressing immediately.
Once you've fixed all the code you can drop VENDOR_NAME from all the dependent tables, and switch VENDOR_NAME to unique key and VENDOR_ID to primary key on the master table.
If you're on 11g you should check out Edition-Based Redefinition. It's designed to make this sort of exercise an awful lot easier. Find out more.
I would do it this way:
create your new sequence
create table temp as select your_sequence.nextval,vendor_name, vendor_contact, comments from vendor.
rename the original table to something like vendor_old
add the primary key and other constraints to the new table
rename the new table to the old name
Testing is essential and you must ensure no one is working on the database except you when this is done.
I have to add some security for a C#/.NET WinForms/Desktop application. I am using Oracle DB back-end.
The tables are simple: User (ID,Name), Role(ID,Role), UserRole(UserID,RoleID).
I am using the windows account name to populate User table. Role table will for now just be simply 'Admin','SuperUser','BasicUser'...
Since no two people could ever possible have the same windows account name... even when I do not control these name management (netops does, hence why I want to use windows accounts so I don't have to manage it ;)). For Role table, I should again never have dupe value - I control the input, there will only be 3 (tactical app going away within year). UserRole is a join table to represent the Many-To-Many relationships of users and roles, so no surragate key is justified.
Simple question - Why bother with 'ID' (int) in the User and Role table? Any point or advantage here? Is this one of those 'I've always done it this way' type things? Or have I just not done this in awhile and forget the reason?
Names change - primary key values must not. Abigail Smith becomes Abigail Jones and the username changes but a surrogate key protects against having to cascade those changes everywhere.
If you are using a surrogate key but there is a column or combination of columns which should be unique, then enforce that using a unique index. There's a good chance you'll want indexes on your user.name and role.role columns anyway, and a unique index is more space efficient and supplies useful metadata to the optimizer. If you have a surrogate key but don't have another combination of columns that uniquely identify a row then think again whether you have your entity definition right.
One caution. Especially for very narrow tables with few access paths, you may use an index-organized table. Oracle will only allow an index organized table on the primary key, but does allow foreign keys against a unique set of columns (if it is enforced by a unique constraint, not simply a unique index).
It is possible that you'll end up with a table where a unique ID is enforced through a unique index and treated as PK by an ORM and used as the parent for foreign key relationships, but the primary key (as defined in the DB) is the rolename/username/whatever because you want that as the driver for an index-organised table.
A surrogate key is not required on intersection tables, but here are a few reasons to do so:
Consistency: If every table has a single artificial key, you always know the key name when you know the table name.
Ease Of Use: Less typing — one key means ON and WHERE clauses are shorter and thus less error-prone.
Interoperability: Some ORMs only work well with tables with a single primary key column.
I have been attempting to use subsonic for a project on which I'm working. All was going quite well until I encountered a link table with a composite primary key. That is a key made up of the primary keys of the two tables it joins. Subsonic failed to recognize both keys which was problematic. I was going to adjust subsonic to support compound keys but I stopped and though "Maybe there is a reason for this". Normally active record relies on a single primary key field for every record, even in link tables. But is this necessary? Should I just give up on active record for this project or continue with my modifications?
Ruby on Rails does not support composite primary keys in model object out of the box. However, there are plugins that accomplish that, for example this.
You can have composite primary key on a join table, but Rails will not create that primary key, you have to create it manually.
See this guide.
How do i use ActiveRecord on existing DB with multiple columns as primary key and no ID column? I had to write extensions/hacks on set_primary_key, update and delete methods. But im not sure if it'll work on future versions. Is there a way to make ActiveRecord work in such cases without hacks?
ActiveRecord doesn't support composite primary keys. Here is a library that purports to add support though.