From 4ba6c26a2151342e3ce479f5f3318f5e1bb5fbc7 Mon Sep 17 00:00:00 2001 From: Philippe PITTOLI Date: Sat, 11 Apr 2020 19:12:57 +0200 Subject: [PATCH] Readme: some fixes, some explanations about deletion base on partition. --- README.md | 41 +++++++++++++++++++++++------------------ 1 file changed, 23 insertions(+), 18 deletions(-) diff --git a/README.md b/README.md index 2347b63..0a62011 100644 --- a/README.md +++ b/README.md @@ -12,7 +12,7 @@ The objective is to get rid of DBMS when storing simple files directly on the fi A brief summary: - no SQL - 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 @@ -81,10 +81,11 @@ require "uuid" class Car include JSON::Serializable - property id : String - property color : String + property id : String + property color : String + property keywords : Array(String) - def initialize(@color) + def initialize(@color, @keywords) @id = UUID.random.to_s end end @@ -120,14 +121,14 @@ storage │   └── 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. -Getting an object by their ID is as simple as `cat storage/indices/by_id/.json`. +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 its ID is as simple as `cat storage/indices/by_id/.json`. 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`: ```Crystal -cars_by_colors = things.new_partition "color", &.color +cars_by_colors = cars.new_partition "color", &.color ``` On the file-system, this translates to: @@ -147,7 +148,7 @@ $ tree storage/ │   └── 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. 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 -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: ```Crystal # we find a car we want to modify @@ -193,25 +194,29 @@ car = cars_by_id "86a07924-ab3a-4f46-a975-e9803acba22d" car.color = "Blue" # 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: ```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 ```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_class.delete "red", do |car| - car.name == "Corvet" || car.keywords.empty +cars_by_color.delete "red" +cars_by_color.delete "red", do |car| + car.keywords.empty 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 ```Crystal @@ -265,7 +270,7 @@ cars << Car.new "SUV", "red", [ "solid", "impressive" ] cars << Car.new "Mustang", "red", [ "shiny", "impressive", "elegant" ] cars << Car.new "Bullet-GT", "red", [ "shiny", "impressive", "fast", "elegant" ] 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 cars.each do |car| @@ -310,9 +315,9 @@ cars_by_name.update_or_create car.name, car # based on a name cars_by_name.delete "Deudeuch" -# based on their color +# based on a color 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") ## TAG-based deletion, soon.