What is the best way to change an existing table with SQLite (add new columns) without losing the table data?
Any time you change a table you have to consider the existing dataset. The data in your DB was created with your old/original table definition and doesn't know anything about the new one. So the data needs to be migrated.
When you migrate a DB, you tell it how to massage the existing data to conform to the new definitions. This often involves inserting a default value, but this isn't a requirement.
There is an excellent (open source) tool that can help you with this process called SQLiteMigrationManager, and it can be found here:
SQLiteMigrationManager.swift (inspired by FMDBMigrationManager)
If you run into any problem be sure to open a new question on this site and I'm sure you will be assisted.
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I am new to Cassandra. I am looking at many examples online. Here is one from JHipster Cassandra examples on GitHub:
https://gist.github.com/jdubois/c3d3bedb869466731316
The repository save(user) method does a read (to look for existence) then a delete and re-insert of the existing user across all the denormalized tables whenever the user data changed.
Is this best practice?
Is this only because of how the data model for this sample is designed?
Is this sample's design a result of twisting a POJO framework into a NoSQL database design?
When would I want to just do a update in Cassandra? It supports updates at the field-level, so it seems like that would be preferred.
First of all, the delete operations should be part of the batch for more robust error handling. But it looks like there are also some concurrency issues with the code. It will update the user based on the current user value read before. It's not save to assume this will still be the latest value while save() is actually executed. It will also just overwrite any keys in the lookup table that might be in use for a different user at that point. E.g. the login could already exist for another user while executing insertByLoginStmt.
It is not necessary to delete a row before inserting a new one.
But if you are replacing rows and new columns are different from existing columns then you need to delete all existing columns and insert new columns. Or insert new and delete old, does not matter if happens in batch.
I am using H2Database With ORMLite. we have 60 tables all created with ORMLite "create if not exists", Now we are going to provide a major release and requirement is to update old version database. But I need to know how to do this with ormLite as in new version some of Tables will be new and some is existing old tables with some modifications e.g we have an table of job in previous version db, in this release we added 2 more columns and change the datatype of one column. any suggestions. I have seen some other posts regarding OrmLite for Android SqlLite. How can this approach be used for other db. e.g Like this post
ORMLite update of the database
But I need to know how to do this with ormLite as in new version some of Tables will be new and some is existing old tables with some modifications e.g we have an table of job in previous version db, in this release we added 2 more columns and change the datatype of one column.
I'm not sure there is any easy answer here. ORMLite doesn't directly provide any magic capabilities to make the migration of data any easier. Here are some thoughts however:
You will need to use some sort of SQL logic to determine whether your application has the "old" or "new" schema installed. You could use raw SQL to look for the existance of particular tables or columns. Might be a good idea going forward to store a meta table with database version which Android gets for free.
You can create new and old versions of each of your entities (OldAccount versus Account) and map them both to the same table with the #DatabaseTable(tableName = "accounts"). Then you can read the old entities using the oldAccountDao.iterator(), convert them to new entities and (as long as you aren't mucking with the primary key) update them using the new accountDao.update(...).
You can certain come up with a series of SQL statements that will need to be performed in the proper order to change the schema. Then call the dao.exectuteRaw(...) with them in order.
Obviously the new entities will just be created.
You might want to consider dumping a backup file of all tables somewhere before the conversion process and telling the user about it in case there is some failure so your users could revert and run the old version of your application.
Hopefully something here is helpful.
I need to insert a field in the middle of current fields of a database table. I'm currently doing this in VB6 but may get the green light to do this in .net. Anyway I'm wondering since Access gives you the ability to "insert" fields in the table is there a way to do this in ADOX? If I had to I could step back and use DAO, but not sure how to do it there either.
If yor're wondering why I want to do this applications database has changed over time and I'm being asked to create Upgrade program for some of the installations with older versions.
Any help would be great.
This should not be necessary. Use the correct list of fields in your queries to retrieve them in the required order.
BUT, if you really need to do that, the only way i know is to create a new table with the fields in the required order, read the data from the old table into the new one, delete the old table and rename the new table as the old one.
I hear you: in Access the order of the fields is important.
If you need a comprehensive way to work with ADOX, your go to place is Allen Browne's website. I have used it to from my novice to pro in handling Access database changes. Here it is: www.AllenBrowne.com. Go to Access Tips then scroll down to ADOX Code.
That is also where I normally refer people with doubts about capabilities of Access as a database :)
In your case, you will juggle through creating a new table with the new field in the right position, copying data to the new table, applying properties to the fields, deleting original table, renaming the new table to the required (original) name.
That is the correct order. Do not apply field properties before copying the data. Some indexes and key properties may not be applied when the fields already have data.
Over time, I have automated this so I just run an application to do detect and implement the required changes for me. But that took A LOT of work-weeks.
I have a CR using multiple Oracle tables with complex links. I have to change the structure of 1 table (add a field actually) but the new structure is not reflected in the crystal report. I have tried refresh or update the location but the newly added field could not be seen. I know there is a not so clever way to "solve" the problem is to delete the table and add it back but by doing that, I will have to recreate the link, rearrange the reports, recreate the calculated fields.... basically rewrite the whole report... any advice to help me quickly update the structure of the my ORACLE table would be highly appreciate.
Thanks,
What you actually need to do is to Verify the database.
Well, found that out ...accidentally. I updated the database location and refreshed it but the new schema was not updated. I decided to run the report anyway... At the time of the report execution, CR realized there was a change in the table structure and updated it! So I think the solution to this is updating the location then execute the report, CR will update it automatically. Do not need to delete the table and added it back because doing so will delete all the links and fields the tables was referring to.
I've been using Core Data for about a week now, and really loving it, but one minor issue is that setting default values requires going through and setting up a temp interface to load the data, which I then do away with once I have the data seeded. Is there any way to edit values in a table, like how you can use phpMyAdmin to manipulate values in a MySQL database? Alternately, is there a way to write a function to import seed values from something like a Numbers spreadsheet if it doesn't detect the storedata XML file?
For your first question, you could edit the file directly but it's highly recommended you don't. How to edit it depends entirely on the store type you selected.
Regarding importing or setting up pre-generated data, of course: you can write code to manually insert entity instances into your Managed Object Context. There's a dedicated section on this very topic in the documentation. Further, if you have a lot of data to import, there's even a section on how to do this efficiently.
Is there any way to edit values in a
table, like how you can use phpMyAdmin
to manipulate values in a MySQL
database?
Xcode has a means of creating a quick and dirty interface for a data model. You just drag the data model file into a window in interface builder and it autogenerates an interface for you. This lets you view the data without having to have your entire app up and running.