I didn't find anything inside the docs. What is the propper way to alter a view in room? I tried with the way to create a migration, drop the existing view and create a new one with the sql text, but I still get the room error with the difference between "expected and found scheme" (even the sql-s seems identical, I checked with a comparison tool)
For everyone, obviously room is comparing raw strings not the table/view that is being generated from the provided sql text/entity. The problem in my case was that I had an extra space after a comma inside my altered view sql text, which led to a false result when comparing to the sql text room was generating from my entity (even though the generated views where the same).
For me it's a little bit of a surprise that room is using the raw sql strings in order to check for integrity..., but now I know.
Edit:
just one tip to always get the exact same sql string. Change the entity as you wish, and compile the app. Even if it crash, room will generate the right sql text for the change that was made inside the entity. Then just open the generated YOURDATABASE_Impl file and search for the table/view.
Related
I am creating an app which needs to show events based on date and time. I imagine it something like this:
For each date, I have time, each of which has something inside. Based on previous project, I started implementation with Room. However I got stuck on my first query with the error that my primary key is not unique. Which makes sense, since am I using #Insert which will add new row with the same ID (the date). How should I organize the DB, so I can have something like the above picture?
How can I get the the first row from first table and add underneath?
Or I should use JSON instead, since my DB won't be that big (I can store in JSONs per month).
I need to change the data type for my SQLite. I am worry that it might effect users who update the App. However, after reading the SQLite document in the following link
https://sqlite.org/datatype3.html
It would seem changing the data type when creating a table column shouldn't break the App. From what I read it seems unlike other SQL database engines, SQLite datatype is associated with the value itself and not the column data type that I initially assigned.
I was going to alter the column data type when user updates the App, but it doesn't seem necessary (nor possible without dropping and recreating table). Am I reading this correctly or am I making a mistake?
The App seems to work well when I test updating, but I want to make sure I am not missing anything. Any feedback is appreciated.
Changing the type name in the column definition can affect the affinity.
This might change the type of some values (for example, attempting to store the string '123' in an INTEGER column will result in the number 123), and might change how comparisons work (WHERE SomeColumn = ? will try to convert the value to the same type as the column's affinity).
So you should change the type name only if you are sure that your app handles the values in this column correctly.
I am trying to create sqllite db for my Android application use
Is it bad habit to have all the data types as text? The reason is even though some data can be integer in nature (like number of items.. Etc) but many times I need to display the values as a string or get it as input from user. So I thought for easier manipulation I will just make the datatype in the db as text
Thoughts?
The first thing to understand here is SQLite Storage Classes. SQLite allows any data type to be stored in a table's columns, the actual data type defined by the table is just a hint to the database engine.
This means that even if you define a column as type INTEGER, you can still store text in it.
That being said, I haven't found a use case for storing arbitrary data types in a column, or a case for disregarding the defined data types. For readability purposes, it would probably be a good idea to type things properly and obey the defined types.
this is more of a question of theory than anything else. I am writing an android app that uses a pre-packaged database. The purpose of the app is solely to search through this database and return values. Ill provide some abstract examples to illustrate my implementation and quandary. The user can search by: "Thing Name," and what I want returned to the user is values a, b, and c. I initially designed the database to have it all contained on a single sheet, and have column 1 be key_index, column 2 be name, column 3 be a, etc etc. When the user searches, the cursor will return the key_index, and then use that to pull values a b and c.
However, in my database "Thing alpha" can have a value a = 4 or a = 6. I do not want to repeat data in the database, i.e. have multiple rows with the same thing alpha, only separate "a" values. So what is the best way to organize the data given this situation? Do I keep all the "Thing Names" in a single sheet, and all the data separately. This is really a question of proper database design, which is definitely something foreign to me. Thanks for your help!
There's a thing called database normalization http://en.wikipedia.org/wiki/Database_normalization. You usually want to avoid redundancy and dependency in the DB entities using a corresponding design with surrogate keys and foreign keys and so on. Your "thing aplpha" looks like you want to have a many-to-many table like e.g. one or many songs belong/s to the same or different genres. You may want to create dictionary tables to hold your id,name pairs and have foreign keys referencing these tables. In your case it will be mostly a read-only DB so you might want to consider creating indexes with high FILLFACTOR percentage don't think sqlite allows it to do though. There're many ways to design the database. Everything depends on the purpose of DB. You can start with a design of your hardware like raids/file systems/db block sizes to match the F-System's block sizes in order to keep the I/O optimal and where to put your tablespaces/filegroups/indexes to balance the i/o load. The whole DB design theory/task is really a deep subject which is not to be underestimated nor is a matter of few sentences in the answer of stackoverflow. :)
without understanding your data better here is my guess at what you are looking for.
table: product
- _id
- name
table: attribute
- product_id
- a
So my fundamentals of creating and manipulating databases are a bit messed up. My aim here is that whenever the app is launched, the user is allowed to specify a table name, and whatever data is then collected is put into that table.
However, I'm confused as to how to do this. Do I simply pass the value of a user entered variable as the table name in my contentprovider class and execute sqlite statements to create it?
I've read/reading the documentation already, so if anyone has any insight or clarity, or even better, code snippets, it would be great.
Why not simply use one table, and create a value that stands for the current app-session, and insert that value with each row. This would make your code simpler, and would still allow you to segregate/filter out the values from a particular app-session. If you want to give the user the ability to enter the value (as you are giving them the ability to choose the table name) you'd just want to check to see if that value had already been used, just as you would have to see if the table-name had already been used.