I have a java, spring-data app that uses Datastore. I need a subset of this data to run analytics using python app. What I need in python app is essentially a join (yup, relational doesnt get out of me) between two "Kinds" queried by key of one kind.
NDB client requires creating same entity models in python to be able to query data, which is a drag. Why cant i simply run the console version of GQL(select * from kind) using python. Maybe I am missing something as this sort of querying is available in almost all relational and nosql DBs.
Your observations are correct: a GQL query cannot perform a SQL-like "join" query. This is documented on the GQL Reference for Python NDB/DB documentation page.
If you would like to submit a feature request to request its implementation, you can simply open an issue for it in the Public Issue Tracker.
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I am building a serveless web app with aws amplify - graphql - dynamodb. I want to know what exactly a scan operation is in this context. For example, I have an User table and queries listUsers and getUser were generated from amplify schema. Are they scan operations or queries?
Thank you for your answers in advance as I could only find the definition of a scan operation but there aren't example for me to identify one when it comes to graphql.
Amplify uses Filter Expressions which are a type of Query.
You can see this yourself by looking at the .vtl files that amplify generates and uploads to appsync.
They are located here: amplify/#current-cloud-backend/api/[API NAME]/build/resolvers
In that folder you can open up one of the Query.list[Model].req.vtl. Even if you are not familiar with Velocity Template Language you can still get the idea. You can see that it uses the expression $util.transform.toDynamoDBFilterExpression.
More info about that util and then looking at the docs for toDynamoDBFilterExpression.
I'm working on a tool that allows Python developers to write pythonic code to interact with a sqlite3 database, similar to sqlalchemy but without the "translation" phase. If I can generate a sqlite3 prepared statement, how can I directly pass it to the evaluation system?
As a rough example, here's how I roughly view a user being able to interact with my tool:
myTable = Table("field1", "field2", "field3")
mytable.insert("foo", "bar", "baz")
select = mytable.select("field1")
---------------
print(select)
>>> ["foo"]
There is no (public) API in SQLite3 that allows you to execute pre-built SQLite bytecode. The bytecode for an SQL statement can be viewed with the EXPLAIN SQL command, but this is meant for debugging and learning purposes, not for what you're trying to do.
And for most purposes, you shouldn't need this. If you feel that the time spent compiling a prepared statement will be a burden, sqlite3_stmt objects can be stored for the lifetime of the sqlite3 database connection it was created with. Prepared statements that have been executed can be reset, allowing them to be executed again. So as long as the database connection exists, you can compile the statement once and use it as many times as you need to.
But that's about it. There is no mechanism to persist a prepared statement beyond the lifespan of the sqlite3 connection. You can't extract the bytecode by any public API, and you can't use some bytecode you've obtained to reconstitute a prepared statement.
If you want persistence beyond the connection, then you need to store the SQL statement text in whatever place you want to be persistent, and then simply recompile the prepared statement when you reconnect to the database. That one recompilation (or many depending on how many you store) shouldn't be a particular burden, depending on the life span of your application.
import { SQLite } from 'expo-sqlite';
export const db = SQLite.openDatabase("db.db");
I tried to use sqlite in the expo and run from a browser, However, I get error TypeError: Illegal invocation, any can help me please
WebSQL API is so bad it was ultimately abandoned as a standard for the web.
The expo-sqlite module provides an SQL database with a WebSQL based interface. This is pretty powerful, and supports pretty much all the features of SQLite. SQLite is also perfect for exactly the kind of use case that apps with offline requirements have. It lets you store large amounts of structured data on disk and read only the parts you need for displaying the current screen into memory.
Maybe you should try #databases/expo
https://itnext.io/using-sqlite-in-expo-for-offline-react-native-apps-a408d30458c3
import connect, {sql} from '#databases/expo';
const db = connect('my-database');
I'm quite new in c# and Xamarin android and I want to backup and restore my offline SQLite database created with sqliteOpenHelper Class, send and use that on another device. thanks in advance.
In Android API sets, the providers for SQLite library are available under, android.database.sqlite package. The most prominent types in the package are:
1. SQLiteOpenHelper: This is the main class that you need to inherit your classes from, in order to handle the database creation, opening or closing events. Even the events such as create new tables, or deleting the old tables and upgrading your databases to a latest version (such as upgrading the schema), are all handled here in this class-derived classes of yours.
2. SQLiteDatabase: This is the object that you get and use to either push the data to the database, or to read the data from the database.
3. SQLiteCursor: This is the cursor implementation for working with the data records that are returned after Query commands.
The way they all communicate is that, the main class for the data manipulation first of all inherits from SQLiteOpenHelperto get the functions to handle, then later has a field of type SQLiteDatabasein it to execute the functions for writing or reading the data.
For more information, you can check:
https://basicsofwebdevelopment.wordpress.com/2017/02/19/learning-sqlite-databases-in-xamarin-for-android/
https://www.c-sharpcorner.com/article/xamarin-android-develop-sqlite-database-using-sqliteopenhelper/
I am trying to process some data from one datastore (from a project A), and write it to another (in project B). My runs are failing with the exception -
com.google.datastore.v1.client.DatastoreException: mismatched databases within request: <unknown!>~projecta vs. <unknown!>~projectb, code=INVALID_ARGUMENT
Is it not possible to do such a thing from cloud dataflow?
I can't really tell what you did from a single error, but you probably tried to save entities from a query from one datastore instance to another. The trouble is the datastore instance id is embedded in each key. So (as a starting point) you should probably create new entity objects using the properties from the query results and save those instead.