Variable

Can be used to assign a value to a variable which can be used within a query.

Variable can be created with READ privileges since they do not modify the collection’s data.

To create a variable, just assign a value to a valid name.

Some valid examples:

  • _ = ...
  • tmp = ...
  • var1 = ...

Variables created within a block become local. They can only be used within the block. See the example below:

a = 'This is a variable!!!';
b = 'Hello';
{
    /* This will create a new variable `a` within this block */
    a = 'New variable within this block';

    /* This will update the global variable `b` */
    b += ' World';
};
[a, b];

Return value in JSON format

[
    "This is a variable!!!",
    "Hello World"
]

Injecting variable

When running a query to ThingsDB, it is possible to inject variables into the code. This is easy, safe, and in some cases even necessary when for example inserting binary data.

Python example:

# inject a variable into the code:
client.query('.a = a;', a=1)

Prevent code injection

Consider you have some user input which is supposed to contain a name, and you want to store that name in ThingsDB.

# Variable `user_input` is supposed to contain a name like `Bob`
client.query(f'.name = "{user_input}";')

Instead of a name, a user could insert something like this: Bob"; .XXX = "This system is hacked!. This would result in the following query statement:

.name = "Bob"; .XXX = "This system is hacked!";

This is very dangerous and definitely not what we want but luckily ThingsDB has a simple solution: variable injection

client.query('.name = inp;', inp=user_input)

Using variable injection we can parse user input in a safe and secure way to ThingsDB.