# Record Filters¶

Filters are a key element of the OpenMW CS user interface, they allow rapid and easy access to records presented in all tables. In order to use this application effectively you need to familiarise yourself with all the concepts and instructions explained in this chapter. The filter system is somewhat unusual at first glance, but once you understand the basics it will be fairly intuitive and easy to use

Filters are a key element to using the OpenMW CS efficiently by allowing you to narrow down the table entries very quickly and find what you are looking for. The filter system might appear unusual at first, you don’t just type in a word and get all instances where it occurs, instead filters are first-class objects in the CS with their own table. This allows you to define very specific filters for your project and store them on disc to use in the next session. The CS allows you fine-grained control, you can choose whether to make a filter persistent between session, only for one session or use a one-off filter by typing it directly into the filter field.

## Terms used¶

Filter
A Filter is generally speaking a tool able to filter the elements of a table, that is select some elements while discarding others, according to some criteria. These criteria are written using their own syntax.
Criterion
A criterion describes some condition a record needs to satisfy in order to be selected. They are written using a special syntax which is explained below. We can logically combine multiple criteria in a filter for finer control.
Expression
Expressions are how we perform filtering. They look like functions in a programming language: they have a name and accept a number of arguments. The expression evaluates to either true or false for every record in the table. The arguments are expressions themselves.
Arity
The arity of an expression tells us how many arguments it takes. Expressions taking no arguments are called nullary, those taking one argument are known as unary expressions and those taking two arguments are called binary.

## Interface¶

Above each table there is a text field which is used to enter a filter: either one predefined by the OpenMW CS developers or one made by you. Another important element is the filter table found under ViewFilters. You should see the default filters made by the OpenMW team in the table. The table has the columns Filter, Description and Modified.

ID
A unique name used to refer to this filter. Note that every ID has a scope prefix, we will explain these soon.
Modified
This is the same as for all the other records, it tells us whether the filter is added or removed. Filters are specific to a project instead of a content file, they have no effect on the game itself.
Filter
The actual contents of the filter are given here using the filter syntax. Change the expressions to modify what the filter returns.
Description
A textual description of what the filter does.

## Using predefined filters¶

To use a filter you have to type its ID into the filter field above a table.

For instance, try to opening the objects table (under the world menu) and type into the filters field project::weapons. As soon as you complete the text the table will show only the weapons. The string project::weapons is the ID of one of the predefined filters. This means that in order to use the filter inside the table you type its name inside the filter field.

Filter IDs follow these general conventions:

• IDs of filters for a specific record type contain usually the name of a specific group. For instance the project::weapons filter contains the term weapons. Plural form is always used.
• When filtering a specific subgroup the ID is prefixed with the name of the more general filter. For instance project::weaponssilver will filter only silver weapons and project::weaponsmagical will filter only magical weapons.
• There are few exceptions from the above rule. For instance there are project::added, project::removed, project::modified and project::base. You might except something more like project::statusadded but in this case requiring these extra characters would not improve readability.

We strongly recommend you take a look at the filters table right now to see what you can filter with the defaults. Try using the default filters first before writing you own.

As mentioned before, filters are just another type of record in the OpenMW CS. To create a new filter you will have to add a new record to the Filters table and set its properties to your liking. Filters are created by combining existing filters into more complex ones.

### Scopes¶

Every default filter has the prefix project. This is a scope, a mechanism that determines the lifetime of the filter. These are the supported scopes:

project::
Indicates that the filter is to be used throughout the project in multiple sessions. You can restart the CS and the filter will still be there.
session::
Indicates that the filter is not stored between multiple sessions and once you quit the OpenMW CS application the filter will be gone. Until then it can be found inside the filters table.

Project-filters are stored in an internal project file, not final content file meant for the player. Keep in mind when collaborating with other modders that you need to share the same project file.

### Writing expressions¶

The syntax for expressions is as follows:

<name>
<name>(<arg1>)
<name>(<arg1>, <arg2>, ..., <argn>)


Where <name> is the name of the expression, such as string and the <arg> are expressions themselves. A nullary expression consists only of its name. A unary expression contains its argument within a pair of parentheses following the name. If there is more than one argument they are separated by commas inside the parentheses.

An example of a binary expression is string("Record Type", weapon); the name is string, and it takes two arguments which are strings of string type. The meaning of arguments depends on the expression itself. In this case the first argument is the name of a record column and the second field is the values we want to test it against.

Strings are sequences of characters and are case-insensitive. If a string contains spaces it must be quoted, otherwise the quotes are optional and ignored.

#### Constant Expressions¶

These expressions take no arguments and always return the same result.

true
Always evaluates to true.
false
Always evaluates to false.

#### Comparison Expressions¶

string(<column>, <value>)

The <value> is a regular expression pattern. The expressions evaluates to true when the value of a record in <column> matches the pattern. Since the majority of the columns contain string values, string is among the most often used expressions. Examples:

string("Record Type", "Weapon")
Will evaluate to true for all records containing Weapon in the Record Type column cell.
string("Portable", "true")
Will evaluate to true [1] for all records containing word true inside Portable column cell.
 [1] There is no Boolean (true or false) value in the OpenMW CS. You should use a string for those.
value(<value>, (<lower>, <upper>))

Match a value type, such as a number, with a range of possible values. The argument <value> is the string name of the value we want to compare, the second argument is a pair of lower and upper bounds for the range interval.

One can use either parentheses () or brackets [] to surround the pair. Brackets are inclusive and parentheses are exclusive. We can also mix both styles:

value("Weight", [20, 50))


This will match any objects with a weight greater or equal to 20 and strictly less than 50.

#### Logical Expressions¶

not <expression>
Logically negates the result of an expression. If <expression> evaluates to true the negation is false, and if <expression> evaluates to false the negation is true. Note that there are no parentheses around the argument.
or(<expr1>, <expr2>, ..., <exprN>)

Logical disjunction, evaluates to true if at least one argument evaluates to true as well, otherwise the expression evaluates to false.

As an example assume we want to filter for both NPCs and creatures; the expression for that use-case is

or(string("record type", "npc"), string("record type", "creature"))


In this particular case only one argument can evaluate to true, but one can write expressions where multiple arguments can be true at a time.

or(<expr1>, <expr2>, ..., <exprN>)

Logical conjunction, evaluates to true if and only if all arguments evaluate to true as well, otherwise the expression evaluates to false.

As an example assume we want to filter for weapons weighting less than a hundred units The expression for that use-case is

and(string("record type", "weapon"), value("weight", (0, 100)))


### Anonymous filters¶

Creating a whole new filter when you only intend to use it once can be cumbersome. For that reason the OpenMW CS supports anonymous filters which can be typed directly into the filters field of a table. They are not stored anywhere, when you clear the field the filter is gone forever.

In order to define an anonymous filter you type an exclamation mark as the first character into the field followed by the filter definition (e.g. !string("Record Type", weapon) to filter only for weapons).

## Creating and saving filters¶

Filters are managed the same way as other records: go to the filters table, right click and select the option Add Record from the context menu. You are given a choice between project- or session scope. Choose the scope from the dropdown and type in your desired ID for the filter. A newly created filter does nothing since it still lacks expressions. In order to add your queries you have to edit the filter record.

### Replacing the default filters set¶

OpenMW CS allows you to substitute the default filter set for the entire application. This will affect the default filters for all content files that have not been edited on this computer and user account.

Create a new content file, add the desired filters, remove the undesired ones and save. Now rename the project file to defaultfilters and make sure the .omwaddon.project file extension is removed. This file will act as a template for all new files from now on. If you wish to go back to the old default set rename or remove this custom file.