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Snapper - Serialize and deserialize relational snapshots
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Snapper 🐡 Coverage Status Build Status

Converts rows from a relational database into serialization snapshots that can be deserialized into new rows at a later time with complex relationships preserved.

Example

From database into the serializer

// Parent table "parents"
[
  "id" => 1,
  "name" => "The parent",
  "favorite_child" => 2 // Note: Circular dependency
],
// Child table "children"
[
  "id" => 1,
  "parent_id" => 1,
  "description" => "I'm child A"
],
// Child table "children"
[
  "id" => 2,
  "parent_id" => 1, // Note: Circular dependency
  "description" => "I'm child B"
]

Out from the serializer

[
  "op" => "INSERT",
  "type" => "parents",
  "rows" => [ 
    [
      "id" => "dee78c67-7c0b-4750-9f44-414f5a45006f",
      "name" => "The parent",
      "favorite_child" => null
    ]
  ]
],
[
  "op" => "INSERT",
  "type" => "children",
  "rows" => [
    [
      "id" => "3d228dca-11e2-43ec-bb03-ea4dace489f7",
      "parent_id" => "dee78c67-7c0b-4750-9f44-414f5a45006f",
      "description" => "I'm child A"
    ],
    [
      "id" => "9eebf63a-69a5-42c7-b1fb-81a5e2058ec9",
      "parent_id" => "dee78c67-7c0b-4750-9f44-414f5a45006f",
      "description" => "I'm child B"
    ]    
  ]
],
[
  "op" => "UPDATE",
  "type" => "parents",
  "rows" => [
    [
      "id" => "dee78c67-7c0b-4750-9f44-414f5a45006f",
      "favorite_child" => "9eebf63a-69a5-42c7-b1fb-81a5e2058ec9"
    ]
  ]
]

Deserialize into database again

INSERT INTO parents (name, favorite_child) VALUES ("The parent", NULL); (LAST_INSERT_ID 555)
INSERT INTO children (parent_id, description) VALUES (555, "I'm child A"); (LAST_INSERT_ID 333)
INSERT INTO children (parent_id, description) VALUES (555, "I'm child B"); (LAST_INSERT_ID 334)
UPDATE parents SET favorite_child = 334 WHERE id = 555;

How to serialize?

<?php
use Prewk\Snapper;

// Define a recipe defining the fields and their references
$r = new Snapper\Recipe;

$recipe = [
  "parents" => $r
    ->primary("id") // Primary key at field "id"
    ->ingredients([
      "name" => $r->value(), // Field "name" is just a value
      // Field "favorite_child" has a circular dependency to the "children" table
      "favorite_child" => $r->circular(
        // Define the relationship and values considered "no relationship"
        $r->ref("children")->optional(null),
        // Fallback to that value until the circular relationship can be resolved
        $r->raw(null)
      ),
    ]),
  "children" => $r
    ->primary("id") // Primary key at field "id"
    ->ingredients([
      "parent_id" => $r->ref("parents"), // Field "parent_id" is referencing the "parents" table
      "description" => $r->value() // Field "description" is just a value
    ])
];

// Create a serializer
$serializer = new Snapper\Serializer(
  new Snapper\Sorter,
  new Snapper\Serializer\SerializationBookKeeper,
  $recipe
);

// Feed the serializer with database rows 
$serializer->add("parents", [
  "id" => 1,
  "name" => "The parent",
  "favorite_child" => 2
]);
$serializer->add("children", [
  "id" => 1,
  "parent_id" => 1,
  "description" => "I'm child A"
]);
$serializer->add("children", [
  "id" => 2,
  "parent_id" => 1,
  "description" => "I'm child B"
]);

// Serialize into a snapshot
$serialization = $serializer->compile()->getOps();

How to deserialize?

<?php
use Prewk\Snapper;

// $recipe = <Same as above>
// $serialization = <The snapshot>
// $dbh = <PDO handle>

// Create inserters
$inserters = [
  "parents" => function(array $rows) use ($dbh) {
    $ids = [];
    
    foreach ($rows as $row) {
      $stmt = $dbh->prepare("INSERT INTO parents (name, favorite_child) VALUES (:name, :favorite_child)");
      $stmt->execute([
        ":name" => $row["name"],
        ":favorite_child" => $row["favorite_child"]
      ]);
    
      $ids[] = $dbh->lastInsertId();        
    }
    
    return $ids;
  },
  "children" => function(array $rows) use ($dbh) {
    $ids = [];
    
    foreach ($rows as $row) {
      $stmt = $dbh->prepare("INSERT INTO children (parent_id, description) VALUES (:parent_id, :description)");
      $stmt->execute([
        ":parent_id" => $row["parent_id"],
        ":description" => $row["description"]
      ]);
    
      $ids[] = $dbh->lastInsertId();
    }
    
    return $ids;
  }
];

// Create updaters
$updaters = [
  "parents" => function(array $rows) use ($dbh) {
    foreach ($rows as $row) {
      $stmt = $dbh->prepare("UPDATE parents SET favorite_child=:favorite_child WHERE id=:id");
      $stmt->execute([
        ":id" => $row["id"],
        ":favorite_child" => $row["favorite_child"]
      ]);
    }    
  },
  "children" => null, // Won't be called in this example
];

// Create a deserializer
$deserializer = new Snapper\Deserializer(
  new Snapper\DeserializationBookKeeper,
  $recipes,
  $inserters,
  $updaters
);

// Deserialize
$deserializer->deserialize($serialization);

Ingredient types

Value

<?php
[
  "foo" => $recipe->value()
]

Pass through the value of the field.

Raw

<?php
[
  "foo" => $recipe->raw(123)
]

Force the value of the field.

Ref

<?php
[
  "foo_id" => $recipe->ref("foos"),
  "bar_id" => $recipe->ref("bars")->optional(0, null)
]

The field is a foreign key that references another table. The optional method takes arguments that, when equal to the encountered field value, is considered non-references and are just passed through like Value.

Morph

<?php
[
  "foo_type" => $recipe->value(),
  "foo_id" => $recipe->morph("foo_type", function(\Prewk\Snapper\Ingredients\Morph\MorphMapper $mapper) {
    return $mapper
      ->on("FOO", "foos")
      ->on("BAR", "bars");
  })->optional(null)
]

Specify a polymorphic relation using two fields, one type (foo_type) and one id (foo_id), and map values in foo_type against other tables.

Requires both fields to be present to function properly, supports optional values that when matched ignores the foreign relation and just passes though the value.

Match

<?php
[
  "type" => $recipe->value(),
  "varies" => $recipe->match("type", function(\Prewk\Snapper\Ingredients\Match\MatchMapper $mapper) us ($recipe) {
    return $mapper
      ->on("FOO", $recipe->ref("foos"))
      ->pattern("/BAR/", $recipe->ref("bars"))
      ->default($recipe->value());
  })
]

Look at the given field (type in the example above) and become different ingredients depending on its value.

  • on: Exact match
  • pattern: Regexp match
  • default: Fallback

If no match is successful and no default is provided, the field will not be included.

Json

<?php
use \Prewk\Snapper\Ingredients\Json;

[
  "data" => $recipe->json(function(Json\JsonRecipe $json) {
    return $json
      // Match { "foo": { "bar": { "baz": <value> } } }
      ->path("foo.bar.baz", function(Json\MatchedJson $matched) {
        return $matched
          ->ref("bazes")->optional(null, 0); // Treat null and 0 as value instead of reference
      })
      // Match { "quxes": [<value>, <value>, <value>, <value>] }
      ->pattern("/quxes\\.\\d+$/", function(Json\MatchedJson $matched) {
        return $matched
          ->ref("quxes");
      })
      // Match { "content": <value> }
      ->path("content", function(Json\MatchedJson $matched) {
        return $matched
          // Match { "content": "Lorem ipsum qux:=123= dolor qux:=456= amet" }
          ->pattern("qux:=(.*?)=", function(
            Json\PatternReplacer $replacer,
            string $replacement
          ) {
            // Here we tell the recipe about what references we found and
            // teach it to search and replace them
            return $replacer->replace(
              "quxes",
              1, // Refers to the index of the resulting preg, so: $matches[1]
              "qux:=$replacement="
            );
          });
      });
  })
]

Define references nested in JSON.

On string and integer refs inside the JSON

The library is built for the normal scenario of integer keys (AUTO_INCREMENT), but when serializing references they will be converted to UUIDS (v4). They are strings that look like this: a0ff60f5-87fe-4d4e-855b-8993f1c3b065.

This poses a problem in JSON when..

{ "foo_id": 123 }

..gets serialized into..

{ "foo_id": "a0ff60f5-87fe-4d4e-855b-8993f1c3b065" }

..and back into a integer key:

{ "foo_id": "456" }

"456" is not strictly equal to 456. Therefore, the deserialization logic is as follows:

  1. If the id returned from the inserter is numeric then all "UUID" will be replaced with INSERT_ID
  2. All UUID will be replaced with INSERT_ID

Circular

<?php
[
  "foo_id" => $recipe->circular(
    $recipe->ref("foos")->optional(0),
    $recipe->raw(0)
  )
]

If two of your tables contain circular references to each other, wrap one of the references with a Circular ingredient. Specify a valid fallback as optional value and specify that value as a fallback Raw ingredient.

The resulting serialization will start with an INSERT op containing the fallback value, and end with an UPDATE op with the real reference.

Events

onDeps

<?php
$deserializer->onDeps("foos", function(string $dependeeType, $dependeeId, $dependencyId) {
  // Every time a dependency of type "foos" has been deserialized, this closure will be called
});

Override recipes/updaters/inserters

<?php

$serializer
  ->setRecipe("foos", $fooRecipe)
  ->setRecipe("bars", $barRecipe);

$deserializer
  ->setRecipe("foos", $fooRecipe)
  ->setInserter("foos", $fooInserter)
  ->setUpdater("foos", $fooUpdater);

Recipe JSON

Recipes can be converted to/from JSON which can be useful.

<?php
use Prewk\Snapper;

$someRecipe = $r->primary("id")->ingredients(["name" => $r->value()]);

$json = json_encode($someRecipe);

file_put_contents("recipe.json", $json);

$json = file_get_contents("recipe.json");

// Note: decode to associative array
$someRecipe = Snapper\Recipe::fromArray(json_decode($json, true));

Validation

Validate a serialization

Check a serialization for unresolvable references

<?php
use Prewk\Snapper;

$validator = new Snapper\Validator(new DeserializationBookKeeper, $recipes);

$isValid = $validator->validate($serialization);

Validate a JSON recipe

Recipes can be validated with a JSON schema validator.

<?php
use Prewk\Snapper;
use JsonSchema\Validator as JsonValidator; // https://github.com/justinrainbow/json-schema

$validator = new Snapper\SchemaValidator(new JsonValidator);

$json = file_get_contents("recipe.json");

// Note: don't decode to associative array
$validator->validate(json_decode($json));

Batched inserts/updates

The insert/update closures will be called with batches of rows that each can be executed in one SQL operation if you want to optimize:

<?php
$inserters = [
  "foos" => function(array $rows) use ($db) {
    $allValues = [];
    $vars = [];
    foreach ($rows as $index => $row) {
      $values = [];

      foreach ($row as $field => $value) {
        $vars[":" . $field . "_" . $index] = $value;
        $values[] = ":" . $field . "_" . $index;
      }

      $allValues[] = "(" . implode(", ", $values) . ")";
    }
    
    /*
     * $rows = [
     *   ["some_field" => "foo", "another_field" => "bar"],
     *   ["some_field" => "baz", "another_field" => "qux"],
     *   ["some_field" => "lorem", "another_field" => "ipsum"]
     * ]
     * 
     * -->
     * 
     * INSERT INTO foos (some_field, another_field) VALUES
     *   ("foo", "bar"),
     *   ("baz", "qux")
     *   ("lorem", "ipsum")
     */
    $insert = "INSERT INTO foos (some_field, another_field) VALUES " . implode(", ", $allValues);
    $stmt = $db->prepare($insert);
    $stmt->execute($vars);
    
    $lastId = $db->lastInsertId();
    
    // If last insert id is 666, then return [664, 665, 666] 
    return range($lastId - count($rows) + 1, $lastId);
  },
];

The following rules apply for the return value from inserters:

  • Returning void is acceptable, but the serialization will fail if later rows depend on the skipped primary keys
  • To return the primary keys, return an array of the same length as $rows, everything else is invalid

The batch grouping logic considers one of the following conditions as "start a new batch of operations":

  • A new row type (table) is encountered
  • The row is dependent on the primary key of another row earlier in the same batch
  • The exact number of, or names of, fields has changed from one row to the next

Id manifest

The result of a compilation ($serializer->compile()) is a Serialization. It has two methods:

  • getOps() - Get an array representing the sequence of operations (the actual "serialization" if you will)
  • getIdManifest() - Get a dictionary mapping the internal uuids in the serialization to your given db ids, grouped by type (table name)

Why?

The library is useful for providing snapshot functionality to multi-tenant services where a user owns one or more complex sets of data with complex internal relationships.

Howtos

I don't want to create table X, it already exists

The deserializer doesn't care about the inserter closure's internal logic, it only requires you to return the primary key:

$somethingId = 123; // Predetermined

$deserializer->setInserter("something", function(array $row) use ($somethingId) {
  // Maybe you don't want to do anything to the database here or maybe
  // you want to do an UPDATE instead of an INSERT - up to you
  
  return $somethingId;
});

I need row metadata to be serialized

Just use $recipe->value() in the recipe and feed whatever fields you want to the Serializer and it'll end up in the snapshot.

When deserializing, pick and choose which fields to insert into the database in your inserter.

I have composite keys

Unsupported at the moment, a workaround is adding a unique id and pretending that's the primary key.

License

MIT

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