What NEXOS does
This page restates what the tutorial checks in the steps, so you can explain it to someone else. It does not add any operation.
The model decides​
You draw the tables and the fields. NEXOS writes the SQL. A new table first lives in the model, with the mark « Por confirmar ». When you click Confirmar, NEXOS compares the model with the real database and applies the changes there.
Depending on the environment​
| Environment | What Confirmar does |
|---|---|
| Desarrollo | Applies only what does not delete data. Removing fields always asks for confirmation. |
| Pruebas | Shows the SQL first, and you are the one who applies it. |
| Producción | Shows the SQL, and also asks you to type the environment name. |
| Solo lectura | Does not touch the database. The refusal stays recorded in Problemas. |
In this tutorial, the connection is in Desarrollo. That is why creating the table, at the Confirm step, did not ask for another click, while removing email was stopped.
Each connection, its database​
A connection shows only the database it points to. The server's other databases are not listed. That is what the tree shows at the step open the database.
All or nothing​
In PostgreSQL, each Confirmar is applied in a transaction. If one statement fails, nothing is left half done.
Never a guessed deletion​
A rename is applied as a rename, and the data stays. Removing a field or a table is never automatic. Tables present in the database but absent from the model are not deleted: they are only reported.
A trace remains​
Each applied change is recorded with its SQL, its time, and its result in the machine's write log.
The other engines​
Today, this path is supported by:
- PostgreSQL, tried during this tutorial;
- SQLite, tried in the automatic tests;
- MySQL, present in the code. The original tutorial marks it as not verified in real conditions: the trial is planned at the close of this first step, which is not described here.
SQL Server and Oracle do not yet create or alter tables from NEXOS: they are read and queried. The original tutorial states that SQL Server arrives at the next step, which is not in this path.