@b08/flat-key, seeded from @b08/library-seed, library type: dry

A set of DRY methods to work with flat key.

reasoning

Most tools like Map from ES6 or groupBy from lodash only work with primitive keys, strings and numbers. They can't work with objects as keys, since 2 objects are not equal unless it is the same object. \
If you want to have a complex key, i.e. 2 or more primitives, you have to devise something like concatenation or serialization. And apply it each time you call one of those functions. \
This library encapsulates key handling.

flat key

I define flat key as an object that can only have primitive properties.
For example, this entity, could have a following key.
``
const entity = {
folder: "./app",
file: "securityEntities.type.ts",
typeName: "User",
fields: [{
name: "userId",
...
}]
};

const entityFlatKey = {
folder: entity.folder,
file: entity.file,
typeName: entity.typeName
};
`
I could also recommend defining such a complex key from the beginning, then entity would look like this:
`
const entity = {
id: {
folder: "./app",
file: "securityEntities.type.ts",
typeName: "User",
},
fields: [{
name: "userId",
...
}]
};
`
This way you don't need to construct new object each time you have to use that key.
Second limitation to the flat key is that all entities of the same type should have the same structure of the key, i.e. no fields can be omitted. This is needed for methods of this library to work properly. Type of key (primitive or flat) and a number of key fields is determined upon encountering first key of the collection.

groupBy


This method groups object by a key, works with both primitive keys or flat object. Returns a KeyGroup object.
`
import { groupBy } from "@b08/flat-key";
const entities = []; // populated somewhere
const grouped = groupBy(entities, e => e.id);
const key = entities[3].id;
const entities3 = grouped.get(key); // all entities that have same flat-key id as entities[3]
`
KeyGroup has following methods:
1. keys() and values() - self explanatory.
2. add(key, item) - adds item against the key.
3. addItem(item) - gets a key using selector then adds it.
4. get(key) - return array of items by the key, null if key is not present.
5. has(key) - returns true if key is present.
6. hasItem(item) - return true if specific item is present. O(n) and reference equality.
7. delete(key) - deletes all items by the key.
8. deleteItem(item) - deletes specific item and returns true if item was present and successfully deleted. O(n) and reference equality.

Can call KeyGroup constructor directly instead of groupBy.

mapBy

Works similar to groupBy, except the key is assigned to only one value. It the same key encountered for the second time, it is overwritten.
Returns KeyMap object. KeyMap has following methods:
1. keys() and values() - self explanatory.
2. add(key, item) - adds item against the key.
3. addItem(item) - gets a key using selector then adds it.
4. get(key) - return item by the key, null if key is not present.
5. has(key) - returns true if key is present.
6. hasItem(item) - return true if specific item is in the store. Reference equality.
7. delete(key) - deletes item by the key.
8. deleteItem(item) - deletes item. Returns true if successfully deleted. Reference equality.

Can call KeyMap constructor directly instead of groupBy.

unique

Returns entities unique by their keys. Key can also be both primitive and flat.
`
const entities = []; // populated somewhere
const filtered = unique(entities, e => e.id);
``
If you want to filter array of keys of repeated keys, omit the selector.

KeySet

Structure similar to Set, except it works by shallow object comparison instead of reference equality. Has following methods.
1. values() - self explanatory.
2. has(item) - returns true if item is present.
3. getOrAdd(item) - adds item to the set, returns this item if it was added, otherwize returns item already existing in the set.
4. delete(item) - deletes item from the set.