Many projects need addition of identical columns to all the tables created by the project. Audit columns are an example of such a requirement. The requirement is to add columns such as created_by, created_date, modified_by and modified_date to all the tables, these columns store, who created the row, when the row was created, who modified the row last and when was it modified. created_by and created_date are required to be present when the row is inserted and thus are required to be not nullable. Adding these columns to each and every table is a lot of work for developers.
In many development shops, developers are not allowed to access the database schema directly, and are not allowed to create tables, indexes, views etc, instead are given access via a different schema that allows SELECT, UPDATE and DELETE access on data. The general reason is to avoid developers creating database objects without
When Behavior Driven Development BDD was introduced, some of the key principles were
- Requirements are behavior,
- Provides “ubiquitous language” for analysis,
- Acceptance criteria should be executable.
- Design constraints should be made into executable tests.
All of these principles can be applied to database development. When interacting with the database, we tend to assume certain behavior of the database. Some of this is universal, like when a row is inserted in a table, the same row can later be retrieved. There are other behaviors of the database on every project that are not that universal, like Person table should have at least firstname or lastname. This behavior changes based on the functionality being developed and thus needs to be properly specified and executed. The database lends itself very well to the new way of thinking in the BDD space, where the behavior of the objects is considered. BDD is similar to describing requirements in code.
IN many projects, there are tables which need default audit columns such as Created_By, Created_Date, Modified_By, Modified_date and other columns that need to be updated everytime some actions are done againt the tables and/or columns. This type of functionality can be implemented using triggers. Why have triggers? when the application can do the updating, this is a good argument, but like all application databases eventually other users, applications and scripts will get access to the applications database and end up wanting to read from the database and write to the database. During these times its better to have triggers updating the data independent of the application to ensure audit columns and other columns are updated with appropriate values.
In every enterprise and every project we end up having multiple environments, especially the database side of the enterprise tends to stick around for a longer period of time and has much more dependencies or application integration as opposed to application urls etc. Given this, how to name the servers, databases and schemas becomes a very important decision, do these names provide for an easy way to use the application and not make it harder or the developers to access the database.
Many of the projects we end up working on are replacing existing systems with existing data either wholly or in part. In all of the above projects we end up writing data migration or data conversion code to move the data from legacy systems to the new systems. Many stake holders of the project such as business users, project managers, business analysts really care about the data conversion scripts and the quality of the conversion. Since this conversion is business entity related and matters a lot as future business/functionality depends on the data being logically equivalent to the legacy system.
Over the years we have found many techniques that help in testing the quality of the data conversion. Here are the 8 techniques that encompass our learnings when converting data over from legacy databases.
In relational database usage the pattern of migrations is well understood and has gained widespread acceptance. Frameworks such as DBDeploy, DBMaintain, MyBatis migrations, Flyway, Liquibase, Active Record Migrations and many others. These tools allow to migrate the database and maintain the version history of the database in the database.
With the rise of NoSQL Databases and their adoption in development teams we are faced with the problem of migrations in NoSQL databases. What are the patterns of data migrations that work in NoSQL databases? as NoSQL databases are schema free and the database does not enforce any schema validation, the schema of the data is in the application and thus allows for different techniques of data migration.
While doing evalauation of NoSQL databases, we had a 10 node riak cluster and wanted check how a similar setup would work with mongodb. So started to setup a 10 node mongodb cluster. Since this was for initial spikes, we decided to set this up on a single machine as with the other test setup using Riak.
Before I explain how we setup 10 node mongodb ReplicaSet, let me talk about replica sets. MongoDB implements replication, providing high availability using replica sets. In a replica set, there are two or more nodes participating in an asynchronous master-slave replication. The replica-set nodes elect the master node, or primary node, among themselves and when the primary node goes down, the rest of the node elect the new primary node.
Its been about a month since my blog moved to octopress, wanted to write about my experience. I had been running my blog for a some time now using Movable Type upgrading as and when new versions where released. Over time I realized that upgrading was fraught with errors as lot of steps had to be done manually. Customizing the layout was risky as there was no way to preview your changes and commit only when I was comfortable. With the release of Movable Type 6 there is no longer a free version to download.
Some versions back, Oracle would not allow to create database object names with mixed cases, even if we tried to create them, we could not. In newer versions of Oracle we can create tables, columns, indexes etc using mixed case or lower case, when the names are put inside double quotes. For example
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