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Readme: some fixes, some explanations about deletion base on partition.

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Philippe PITTOLI 2020-04-11 19:12:57 +02:00
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README.md
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@ -12,7 +12,7 @@ The objective is to get rid of DBMS when storing simple files directly on the fi
A brief summary: A brief summary:
- no SQL - no SQL
- objects are serialized (currently in JSON) - objects are serialized (currently in JSON)
- indexes (simple soft links on the FS) can be created to improve significantly searches in the db - indexes (simple symlinks on the FS) can be created to improve significantly searches in the db
## Limitations ## Limitations
@ -83,8 +83,9 @@ class Car
include JSON::Serializable include JSON::Serializable
property id : String property id : String
property color : String property color : String
property keywords : Array(String)
def initialize(@color) def initialize(@color, @keywords)
@id = UUID.random.to_s @id = UUID.random.to_s
end end
end end
@ -120,14 +121,14 @@ storage
│   └── 8b4e83e3-ef95-40dc-a6e5-e6e697ce6323.json -> ../../data/0000000001.json │   └── 8b4e83e3-ef95-40dc-a6e5-e6e697ce6323.json -> ../../data/0000000001.json
``` ```
We have 5 objects in the DB, each of them have a unique ID attribute, each attribute is related to a single object. We have 5 objects in the DB, each of them has a unique ID attribute, each attribute is related to a single object.
Getting an object by their ID is as simple as `cat storage/indices/by_id/<id>.json`. Getting an object by its ID is as simple as `cat storage/indices/by_id/<id>.json`.
Now we want to sort cars based on their `color` attribute. Now we want to sort cars based on their `color` attribute.
This time, we use a `partition`, because the relation between the attribute (color) and the object (car) is `1-n`: This time, we use a `partition`, because the relation between the attribute (color) and the object (car) is `1-n`:
```Crystal ```Crystal
cars_by_colors = things.new_partition "color", &.color cars_by_colors = cars.new_partition "color", &.color
``` ```
On the file-system, this translates to: On the file-system, this translates to:
@ -147,7 +148,7 @@ $ tree storage/
│   └── 0000000005.json -> ../../../data/0000000005.json │   └── 0000000005.json -> ../../../data/0000000005.json
``` ```
Now the attribute correspond to a directory (blue, red, violet, etc.) containing a symlink for each related object. Now the attribute corresponds to a directory (blue, red, violet, etc.) containing a symlink for each related object.
Finally, we want to sort cars based on the `keywords` attribute. Finally, we want to sort cars based on the `keywords` attribute.
This is a n-n relation, each car may have several keywords, each keyword may be related to several cars. This is a n-n relation, each car may have several keywords, each keyword may be related to several cars.
@ -183,7 +184,7 @@ This is very similar to partitions, but there is a bit more complexity here sinc
## Updating an object ## Updating an object
In our last example we had a `Car` class, we stored its instances in `cars` and we could identify each instance by its `id` with the index `car_by_id`. In our last example we had a `Car` class, we stored its instances in `cars` and we could identify each instance by its `id` with the index `cars_by_id`.
Now, we want to update a car: Now, we want to update a car:
```Crystal ```Crystal
# we find a car we want to modify # we find a car we want to modify
@ -193,25 +194,29 @@ car = cars_by_id "86a07924-ab3a-4f46-a975-e9803acba22d"
car.color = "Blue" car.color = "Blue"
# update # update
cars_by_id.update "86a07924-ab3a-4f46-a975-e9803acba22d", car cars_by_id.update car.id, car
``` ```
Or, in the case the object may not yet exist: Or, in the case the object may not yet exist:
```Crystal ```Crystal
cars_by_id.update_or_create "86a07924-ab3a-4f46-a975-e9803acba22d", car cars_by_id.update_or_create car.id, car
``` ```
## Removing an object ## Removing an object
```Crystal ```Crystal
cars_by_id.delete "86a07924-ab3a-4f46-a975-e9803acba22d", car cars_by_id.delete "86a07924-ab3a-4f46-a975-e9803acba22d"
cars_by_class.delete "red" cars_by_color.delete "red"
cars_by_class.delete "red", do |car| cars_by_color.delete "red", do |car|
car.name == "Corvet" || car.keywords.empty car.keywords.empty
end end
``` ```
In this last example, we apply the function on red cars only.
This represents a performance boost compared to applying the function on all the cars.
# Complete example # Complete example
```Crystal ```Crystal
@ -265,7 +270,7 @@ cars << Car.new "SUV", "red", [ "solid", "impressive" ]
cars << Car.new "Mustang", "red", [ "shiny", "impressive", "elegant" ] cars << Car.new "Mustang", "red", [ "shiny", "impressive", "elegant" ]
cars << Car.new "Bullet-GT", "red", [ "shiny", "impressive", "fast", "elegant" ] cars << Car.new "Bullet-GT", "red", [ "shiny", "impressive", "fast", "elegant" ]
cars << Car.new "GTI", "blue", [ "average" ] cars << Car.new "GTI", "blue", [ "average" ]
cars << Car.new "Deudeuch", "violet", [ "dirty", "slow", "only french will understand" ] cars << Car.new "Deudeuch", "violet", [ "dirty", "slow", "only French will understand" ]
# The DB can be accessed as a simple array # The DB can be accessed as a simple array
cars.each do |car| cars.each do |car|
@ -310,9 +315,9 @@ cars_by_name.update_or_create car.name, car
# based on a name # based on a name
cars_by_name.delete "Deudeuch" cars_by_name.delete "Deudeuch"
# based on their color # based on a color
cars_by_color.delete "red" cars_by_color.delete "red"
# based on their color (but not only) # based on a color (but not only)
cars_by_color.delete "blue", &.name.==("GTI") cars_by_color.delete "blue", &.name.==("GTI")
## TAG-based deletion, soon. ## TAG-based deletion, soon.