I am using Entity Framework to handle the database in a server application. The server application is deployed to multiple nodes sitting behind a load balancer. I have now discovered the need to rename some of the tables and some of the table columns in the database. The problem is that I will need to do this without any down-time.
If I was writing my own database layer I could simply check the structure of the database and then run different code depending on if the database structure was upgraded or not and then I could potentially have 0% downtime.
Is it possible to do something like this in entity framework 4 or how do I actually make database changes in production with entity framework? I have searched the web for any solution but to no success. I have also considered having 2 entity framework instances in my app but the amount of code I have to write to switch between them would be far too much and error prone.
So to summarize the question:
Is there any way to rename tables and columns in a database in a production environment using Entity Framework 4 and without any downtime whatsoever?
EDIT
A new idea I got would be to create a view in place of the old table with the old naming scheme referencing the new table. I dont know if this will work. For it to work Entity Framework needs to accept this view like it would be a normal table. Could this be a good idea? Anyone tried anything like this with EF4 ?
Okay! Here is what thought I got -
Create new table in DB than renaming and build EntityFramework solution on that.
You need to deploy this by taking one server off from loadbalancer, update it,point entity framework code to new table structure and then again attach to loadbalancer.
Make the same procedure for all the servers in loadbalancer one by one. Once all are up with updated patch then sync old table and new table and then just delete old table. I am suggesting synching these tables so that you have all the data without data loss might happen in above process.
Related
I have a database which is used by multiple projects. Each project has its database migration.
I have tried to google and read the knex documentation, but no luck. I have seen some suggestion to fake the migration files to trick the migration table, but I don't think it is a good solution.
I want to keep all the migrations data in one migration table. Is it possible on knex?
Having different set of migration files for each projects and trying to run them separately against the same migration table is not possible. There is no good solution for it and it would not make sense anyways to do it.
If migrations are not related to each other, then there is no reason to have them in the same table. On the other hand if they are related, then the files really should be hosted in the same place to guarantee that everything is done in correct order.
You can setup migration table name tableName (http://knexjs.org/#Migrations-API) to be different for every project in knex config.
However I would never recommend having multiple projects using the same database and everyone having separate migrations for it.
Only reason where that could be remotely acceptable would be the case where you don't have access to create separate databases for each project.
If projects are sharing the same data model (microservices with shared DB), in that case you should still be using multiple databases or to have single service which is the owner of the schema changes and the rest of the services should only read/write data.
I'm kinda new to this kind of problem. I'm developing a web-app and changing DB design trying to improve it and add new tables.
well since we had not published the app since some days ago,
what I would do was to dump all the tables in server and import my local version but now we've passed the version 1 and users are starting to use it.
so I can't dump the server, but I still would need to update design of server DB when I want to publish a new version. What are the best practices here?
I like to know how I can manage differences between local and server in mysql?
I need to preserve data in server and just change the design, data on local DB are only for test.
Before this all my other apps were small and I would change a single table or column but I can't keep track of all changes now, since I might revert many of them later and managing all team members on this is impossible.
Assuming you are not using a framework that provides a migration tool for database, you need to keep track of the changes manually.
Create a folder sql_upgrades (or whatever name you name) in your code repository
Whenever a team member updates the SQL schema, he creates a file in this folder with the corresponding ALTER statements, and possibly UPDATE, CREATE TABLE etc. So basically the file contains all the statements used to update the dev database.
Name the files so that it's easy to manage, and that statements for the same feature are grouped together. I suggest something like YYYYMMDD-description.sql, e.g. 20150825-queries-for-feature-foobar.sql
When you push to production, execute the files to upgrade you SQL schema in production. Only execute the files that have been created since your last deployment, and execute them in the order they have been created.
Should you need to rollback a file, check the queries it contains, and write queries to undo what was done (drop added columns, re-create dropped columns, etc.). Note that this is "non-trivial", as many changes cannot be rolled back fully (e.g. you can recreate a dropped column, but you will have lost the data inside).
Many web frameworks (such as Ruby of Rails) have tools that will do exactly that process for you. They usually work together with the ORM provided by the framework. Keeping track of the changes manually in SQL works just as well.
I am continuing the development of an android app that works against a server using maven, springframework and server database is MySQL.
need 2 very specific things:
I want to create a table
I want to create a trigger
But I want to create from springframework and maven and I could not find a way to do it.
Since it is a project among several people I want to be as automatic as possible to keep things simple.
I want to start when the server maven can create the table and the trigger if there are not exist.
It will be done?
I would like a simple example or a site I can visit and give me at least the concept of how.
Maven is a tool which builds your application. It's not available when the application runs. Therefore, it's often not the best choice to create database tables, etc.
A better approach is to locate the place where Spring's ApplicationContext is created and add code there that examines the database, finds out which tables already exist and create those which don't.
Later, you can extend the code to migrate data when your data model changes.
To execute SQL, check the Spring JDBC documentation and especially JdbcTemplate.
I'm working with a project which is using mysql as the database. The application is hosted with many clients and we are doing upgrades for the current live systems often.
There are some instances where the client has change the database structure(adding new tables) and causes some unexpected db crashes.
I need to log all the structural changes which were done at that database, so we can find the correct root cause for that. We can't do it 100% correct with diff tool because it will not show the intermediate changes.
I found http://www.liquibase.org/ tool but seems little bit complex.
Is there any well known technique or a tool to track database structural changes only.
well from mysql studio you can generate all object's schema definition and compare them with your standard schema definition and this way you can compare two database schema...
generate scrips of both database (One is client's Database and One is master copy database) and then compare it using file compare tool would be the best practice according to me because this way you can track which collumn was added, which column was deleted, which index was added like wise without any tool download.
Possiable duplication of Compare two MySQL databases ?
Hope this helps.
If you have an application for your clients to manage these schema changes, you can use a mechanism at application level. If you have a Python and Django-based solution, you could probably use South which provides schema change tracking and rollbacks.
I'm currently putting together (on old fashioned paper) a layout for my new database, but was told I should probably lay it out as a scheme, which is true.
Is there a tool that allows me to create my table structure/scheme in a plan type layout interface with all relationships and when it's finished it automagically creates the tables in the database and spits out the schema as a file I can print and share with others?
MySQL Workbench sounds like just the ticket.