I am looking for a way to get a unique ID per database itself. The idea is to exchange objects between different installations of my application. Therefore I have unique IDs for all objects within a single database, but in order to exchange these objects to other databases with the same schema, I introduced a composite ID consisting of a primary and a secondary ID, where the primary is unique within a single database and the secondary should be unique across multiple databases with the same schema.
Does somebody knows a decentralized solution for this issue?
Using a global unique identifier for each row solves the problem. Java itself provides a UUID generator, but there are more (better) third-party generators as well.
Related
We are implementing Services Oriented Architecture (SOA). We have different service databases for each, Customer Management, Orders, Shipping, Refunds. What is strategies to maintain foreign key relationships across tables in different databases (since cross database foreign keys are not allowed in SQL Server)? Should foreign keys be substituted with business API rules?
This is not Microservices; where database information is replicated in each arena, but SOA. We did not want put everything in 1 database, since different backup maintenance hours, did not want deadlock/runaway query to bring down all services. Service Oriented Architecture does not dictate if we should have 1 database or multiple.
You can use a Guid(UUID) as the key of your entities, generated by the creator and then you can use that Guid across databased and tables to reference the entity in question.
for example, when you create a new order, the ui will generate the order's Id, send a message to the component creating the order, the component will then publish an event using that orderId so that the other components can do related work to that order without accessing the database to get that id.
Make sense?
I am evaluating outsystems and am trying to write a PoC List/CRUD app based on a legacy database table (the structure of which cannot be changed) which does not have a primary key but instead has two text fields that together constitute a unique index. The database is SQL Server 2014.
The table is successfully added in Integration Studio using "Connect to External table or view".
Then when I open the TestApp in Service Studio and go to the data tab I see the entity there, but it's not usable because it has no identifier defined. I have read some online info that I can double click on the entity and go to the Indexes tab. Here I normally would expect to see the index already defined in the database but it's not there. I also expect to the the New and Delete buttons to be enabled so I can create and delete indexes but New is disabled.
Am I correct to assume that OutSystems should have already "seen" the existing composite unique index? If so, am I correct to assume that this index would have sufficed to create a pseudo/virtual identifier for the entity, whereby making the entity system happy for CRUD and List operations? And also why is the New button not enabled for me to even manually create the index?
Can someone help me please in the correct direction?
Thanks
The OutSystems platform only supports single primary keys, so you have to create the CRUD operations by hand.
For external entities, index information is not fetched from the database, and the reason you can't create the index is because OutSystems doesn't control the metadata (i.e. you can't create indexes, create/modify columns, etc).
I have an existing product using the increment ID generator for most db entities. A new version should allow clustering of multiple server instances working on the same database. The product supports use of MSSQL and Oracle databases.
So I consider changing the ID generator to native, but there are some issues with that.
Two different algorithms will be used for Oracle and MSSQL - will that be transparent when creating objects in the code?
How can I migrate existing databases and how will I get the generator to not use the IDs already in use?
Thanks in advance for any insights on this.
I would suggest looking at a hilo generator strategy. The benefit is that it can be used for multiple processes, and you still retain the performance benefit of using a generated id in NHibernate (specifically allowing batching of inserts).
MSSQL does not allow you to change a column to be an identity column - you will need to add a new column and then update all the foreign keys - if you have a lot of tables / relationships, this can be very very messy.
With the hilo generator strategy you can avoid that issue altogether, it's just a configuration change and adding a table to your database to store the table high values, and populating that table with the correct values.
What's the best practice for handling primary keys using an ORM over Oracle or SQL Server?
Oracle - Should I use a sequence and a trigger or let the ORM handle this? Or is there some other way ?
SQL Server - Should I use the identifier data type or somehow else ?
If you are using any kind of ORM, I would suggest you to let it handle your primary keys generation. In SQL Server and Oracle.
With either database, I would use a client-generated Guid for the primary key (which would map to uniqueidentifier in SQL Server, or RAW(20) in Oracle). Despite the performance penalty on JOINs when using a Guid foreign key, I tend to work with disconnected clients and replicated databases, so being able to generate unique IDs on the client is a must. Guid IDs also have advantages when working with an ORM, as they simplify your life considerably.
It is a good idea to remember that databases tend to have a life independent from a front end application. Records can be inserted by batch processes, web services, data exchange with other databases, heck, even different applications sharing the same database.
Consequently it is useful if a database table is in charge of its own identify, or at least has that capability. For instance, in Oracle a BEFORE INSERT trigger can check whether a value has been provided for its primary key, and if not generate its own.
Both Oracle and SQL Server can generate GUIDs, so that is not a sufficient reason for delegating identity generation to the client.
Sometimes, there is a natural, unique identifier for a table. For instance, each row in a User table can be uniquely identified by the UserName column. In that case, it may be best to use UserName as the primary key.
Also, consider tables used to form a many to many relationship. A UserGroupMembership table will contain UserId and GroupId columns, which should be the primary key, as the combination uniquely identifies the fact that a particular user is a member of a particular group.
Our application architecture allows us to host multiple clients in a single database, and also host multiple databases. This allows us to scale out by distributing clients across multiple databases. For example, 20 clients can be in database A, and another 15 could be in database B. We use a ClientID field in almost every table to partition client data. All our table's primary keys are INT identity TableID fields.
I'm looking for a tool/script that would help me extract client data from one database, and move it to a brand new database (so the PKs can stay the same). I'm hoping this exists already so we don't have to build our own. Pretty flexible in how this could work, but ideally it just generates a large .sql file with all the necessary INSERTS in the right order to move the data, and another sql file with all the necessary DELETES to erase the data from the source.
If it makes any difference we are on SQL Server 2008.
If you have standard or enterprise, you do have SSIS. Although it may not qualify as a "tool", it is fairly easy to implement in this scenario.
I can recomend redgate SQL DataCompare for this, we use it for syncing data, and use their SQL Compare to sync the database schema.
Both tools can either output sql, you can execute yourself, or the tools can execute the sql scripts themself.
They have a command line version of the tools to, so you could use them in an deployment script, tho i haven't tried this.
They both work really well, and are no doubt worth the price.
Not the answer you may be looking for, but you should consider using a GUID as a key. This will ensure that you have some type of unique identifier for your all records and that you can avoid collisions with identity keys / integer based indexes. It would add another degree of traceability should something go wrong when you migrate between databases.
SplendidCRM uses this technique when importing data from other DB systems.
Update:
My assumption was that the operation of transferring data between databases was not that frequent and that you needed database architecture for that task. I would use the GUID as lookup key specifically validation for the transfer of data, but I would NOT use that as a primary key for joins for standard operations like URL's. Although unique across databases, the trade-off is that GUIDs are slow.
In other words, the GUIDS would in addition to your existing primary keys now, and act as a means of validation for you should something go wrong. If you need ClientID in Database A to retain the same value in Database B then an identity column as that identifier will be an issue. You may have to create another identifier that is not "auto-generated". This could something other than the GUID, but my instinct is that integers alone will not be enough. Maybe you can create a columns that is a hash of the identity key, customer name and database name, or more simply, just concatenate those columns into a varchar column.