11. Searching for things

We have gone through how to create the various entities in Evennia. But creating something is of little use if we cannot find and use it afterwards.

To test out the examples in this tutorial, let’s create a few objects we can search for in the current location.

> create/drop Rose 

11.2. Main search functions

The base search tools of Evennia are the evennia.search_* functions, such as evennia.search_object. These are normally used in your code, but you can also try them out in-game using py:

 > py evennia.search_object("rose")
 <Queryset [Rose]>

This searches for objects based on key or alias. The .search method we talked about in the previous section in fact wraps evennia.search_object and handles its output in various ways. Here’s the same example in Python code, for example as part of a command or coded system:

import evennia 

roses = evennia.search_object("rose")
accts = evennia.search_account("YourName")

Above we find first the rose and then an Account. You can try both using py:

> py evennia.search_object("rose")[0]
> py evennia.search_account("YourName")[0]
<Player: YourName>

In the example above we used [0] to only get the first match of the queryset, which in this case gives us the rose and your Account respectively. Note that if you don’t find any matches, using [0] like this leads to an error, so it’s mostly useful for debugging.

If you you really want all matches to the search parameters you specify. In other situations, having zero or more than one match is a sign of a problem and you need to handle this case yourself. This is too detailed for testing out just with py, but good to know if you want to make your own search methods:

    the_one_ring = evennia.search_object("The one Ring")
    if not the_one_ring:
        # handle not finding the ring at all
    elif len(the_one_ring) > 1:
        # handle finding more than one ring
        # ok - exactly one ring found
        the_one_ring = the_one_ring[0]

There are equivalent search functions for all the main resources. You can find a listing of them in the Search functions section of the API front page.

11.3. Understanding object relationships

It’s important to understand how objects relate to one another when searching.

Let’s consider a chest with a coin inside it. The chest stands in a dungeon room. In the dungeon is also a door (an exit leading outside).

│dungeon                │
│    ┌─────────┐        │
│    │chest    │ ┌────┐ │
│    │  ┌────┐ │ │door│ │
│    │  │coin│ │ └────┘ │
│    │  └────┘ │        │
│    │         │        │
│    └─────────┘        │
│                       │

If you have access to any in-game Object, you can find related objects by use if its .location and .contents properties.

  • coin.location is chest.

  • chest.location is dungeon.

  • door.location is dungeon.

  • room.location is None since it’s not inside something else.

One can use this to find what is inside what. For example, coin.location.location is the dungeon.

  • room.contents is [chest, door]

  • chest.contents is [coin]

  • coin.contents is [], the empty list since there’s nothing ‘inside’ the coin.

  • door.contents is [] too.

A convenient helper is .contents_get - this allows to restrict what is returned:

  • room.contents_get(exclude=chest) - this returns everything in the room except the chest (maybe it’s hidden?)

There is a special property for finding exits:

  • room.exits is [door]

  • coin.exits is [] since it has no exits (same for all the other objects)

There is a property .destination which is only used by exits:

  • door.destination is outside (or wherever the door leads)

  • room.destination is None (same for all the other non-exit objects)

11.4. What can be searched for

These are the main database entities one can search for:

Most of the time you’ll likely spend your time searching for Objects and the occasional Accounts.

Most search methods are available directly from evennia. But there are also a lot of useful search helpers found via evennia.search.

So to find an entity, what can be searched for?

11.4.1. Search by key

The key is the name of the entity. Searching for this is always case-insensitive.

11.4.2. Search by aliases

Objects and Accounts can have any number of aliases. When searching for key these will searched too, you can’t easily search only for aliases. Let’s add an alias to our rose with the default alias command:

> alias rose = flower

Alternatively you can achieve the same thing manually (this is what the alias command does for you automatically):

> py self.search("rose").aliases.add("flower")

If the above example rose has a key "Rose", it can now also be found by searching for its alias flower.

> py self.search("flower")

All default commands uses the same search functionality, so you can now do look flower to look at the rose as well.

11.4.3. Search by location

Only Objects (things inheriting from evennia.DefaultObject) has a .location property.

The Object.search method will automatically limit its search by the object’s location, so assuming you are in the same room as the rose, this will work:

> py self.search("rose")

Let’s make another location and move to it - you will no longer find the rose:

> tunnel n = kitchen
> py self.search("rose")
Could not find "rose"

However, using search_object will find the rose wherever it’s located:

 > py evennia.search_object("rose") 
 <QuerySet [Rose]> 

The evennia.search_object method doesn’t have a location argument. What you do instead is to limit the search by setting its candidates keyword to the .contents of the current location. This is the same as a location search, since it will only accept matches among those in the room. In this example we’ll (correctly) find the rose is not in the room.

> py evennia.search_object("rose", candidate=here.contents)
<QuerySet []>

In general, the Object.search is a shortcut for doing the very common searches of things in the same location, whereas the search_object finds objects anywhere.

11.4.4. Search by Tags

Think of a Tag as the label the airport puts on your luggage when flying. Everyone going on the same plane gets a tag, grouping them together so the airport can know what should go to which plane. Entities in Evennia can be grouped in the same way. Any number of tags can be attached to each object.

Go back to the location of your rose and let’s create a few more plants:

> create/drop Daffodil
> create/drop Tulip
> create/drop Cactus

Then let’s add the “thorny” and “flowers” tags as ways to group these based on if they are flowers and/or have thorns:

py self.search("rose").tags.add("flowers")
py self.search("rose").tags.add("thorny")
py self.search("daffodil").tags.add("flowers")
py self.search("tulip").tags.add("flowers")
py self.search("cactus").tags.add("flowers")
py self.search("cactus").tags.add("thorny")	

You can now find all flowers using the search_tag function:

py evennia.search_tag("flowers")
<QuerySet [Rose, Daffodil, Tulip, Cactus]>
py evennia.search_tag("thorny")
<QuerySet [Rose, Cactus]>

Tags can also have categories. By default this category is None , which is considered a category of its own. Here are some examples of using categories in plain Python code (you can also try this out with py if you want to create the objects first):

silmarillion.tags.add("fantasy", category="books")
ice_and_fire.tags.add("fantasy", category="books")
mona_lisa_overdrive.tags.add("cyberpunk", category="books")

Note that if you specify the tag with a category, you must also include its category when searching, otherwise the tag-category of None will be searched.

all_fantasy_books = evennia.search_tag("fantasy")  # no matches!
all_fantasy_books = evennia.search_tag("fantasy", category="books")

Only the second line above returns the two fantasy books.

all_books = evennia.search_tag(category="books")

This gets all three books.

11.4.5. Search by Attribute

We can also search by the Attributes associated with entities.

For example, let’s say our plants have a ‘growth state’ that updates as it grows:

> py self.search("rose").db.growth_state = "blooming"
> py self.search("daffodil").db.growth_state = "withering"

Now we can find the things that have a given growth state:

> py evennia.search_object("withering", attribute_name="growth_state")
<QuerySet [Rose]> 

Searching by Attribute can be very practical. But if you want to group entities or search very often, using Tags and search by Tags is faster and more resource-efficient.

11.4.6. Search by Typeclass

Sometimes it’s useful to limit your search by which Typeclass they have.

Let’s say you for example have two types of flower, CursedFlower and BlessedFlower defined under mygame/typeclasses.flowers.py. Each class contains custom code that grants curses and blessings respectively. You may have two rose objects, and the player doesn’t know which one is the bad or the good one. To separate them in your search, you can make sure to get the right one like this (in Python code)

cursed_roses = evennia.search_object("rose", typeclass="typeclasses.flowers.CursedFlower")

If you e.g. have the BlessedRose class already imported you can also pass it directly:

from typeclasses.flowers import BlessedFlower
blessed_roses = evennia.search_object("rose", typeclass=BlessedFlower)

A common use case is finding all items of a given typeclass, no matter what they are named. For this you don’t use search_object, but search with the typeclass directly:

from typeclasses.objects.flowers import Rose
all_roses = Rose.objects.all()

This last way of searching is a simple form of a Django query. This is a way to express SQL queries using Python. See the next lesson, where we’ll explore this way to searching in more detail.

11.4.7. Search by dbref

The database id or #dbref is unique and never-reused within each database table. In search methods you can replace the search for key with the dbref to search for. This must be written as a string #dbref:

the_answer = self.caller.search("#42")
eightball = evennia.search_object("#8")

Since #dbref is always unique, this search is always global.


Relying on #dbrefs

In legacy code bases you may be used to relying a lot on #dbrefs to find and track things. Looking something up by #dbref can be practical - if used occationally. It is however considered bad practice to rely on hard-coded #dbrefs in Evennia. Especially to expect end users to know them. It makes your code fragile and hard to maintain, while tying your code to the exact layout of the database. In 99% of use cases you should organize your code such that you pass the actual objects around and search by key/tags/attribute instead.

11.5. Summary

Knowing how to find things is important and the tools from this section will serve you well. These tools will cover most of your regular needs.

Not always though. If we go back to the example of a coin in a chest from before, you could use the following to dynamically figure out if there are any chests in the room with coins inside:

from evennia import search_object

# we assume only one match of each 
dungeons = search_object("dungeon", typeclass="typeclasses.rooms.Room")
chests = search_object("chest", location=dungeons[0])
# find if there are any skulls in the chest 
coins = search_object("coin", candidates=chests[0].contents)

This would work but is both quite inefficient, fragile and a lot to type. This kind of thing is better done by directly querying the database.

In the next lesson we will dive further into more complex searching when we look at Django queries and querysets in earnest.