Avoiding duplicate content in Magento's EAV model

Magento’s (1+2) EAV (Entity-Attribute-Value) database model allows too much redundant data. This leads to an unusual large database and strains errors when working with that data in the backend. Taking care of the shop content is for most merchants a pretty huge task. In this post I would like to propose an overall fix to this problem with backwards incompatible changes to the database structure.

TODO: Fix grammar.

Even if you use a PIM (Product Information Management) the amount of data is still the same. The PIM connector does all the work to push the data into Magento. The database will be slowed down.

Magento’s customers, price structure and stock handling affects this issue too. We remove those limitations.

With the following proposed changes a PIM might become superfluous ;-) and we gain overall flexibility with customers, prices and stocks.

Intro and wording

Magento itself states different confusing names in the backend for the overall scope setting. We stick here to the database table names:

  • Admin -> Default
  • Website -> Website
  • Store -> Group
  • Store View -> Store
Magento Backend Scope Our wording for Scope
Admin Default
Website Website
Store Group
Store View Store

The hierarchy level goes always from the highest (Default) to the lowest and most granular (Store).

Default -> Website -> Group -> Store

The simplified database schema of those three tables are:

Magento Scope Schema

Possible scopes for Magento Configuration settings
Config Setting Default Website Store Group Store View
Product settings X X
Product prices X X
Product tax class X X
Base currency X X
(Default) display currency X X
Category settings X X
System configuration settings X X X
Root category configuration X
Orders X
Customers X X

As you can set a lot of settings cannot be applied to another scope, despite you need sometimes!

Even scopes which can officially only be applied on the website level will be finally stored on store level.

EAV Database Architecture

I pick a random EAV type table catalog_product_entity_varchar and its parent catalog_product_entity table where you can see in the entity type table that the column store_id is mandatory. The schema has been simplified.

Magento Catalog Product Simple Schema

Also in the tier_price table you can see the website_id column, same “architectural bug” as the store_id column.

In total the EAV schema exists of 7 tables:

  • catalog_product_entity_datetime
  • catalog_product_entity_decimal
  • catalog_product_entity_int
  • catalog_product_entity_text
  • catalog_product_entity_varchar
  • catalog_product_entity_tier_price (special)

The challenge

Most Magento stores I’ve implemented, and have seen, work with the country as website scope, group scope unused and on the store level the language for a country. Even Magento itself suggests this kind of setup for multi language stores. This looks in a current production store like:

Magento Multi Language Store Setup

To summarize the used languages:

  • 6x English
  • 5x German
  • 4x French
  • 2x Italian

If we reflect the EAV database schema you can imagine that each language specific text/description/setting must be stored the number of times the language gets used.

Usually this will be done via an import module which copies all the data into the database. But if you’re not in the luck to rely on the imported data from e.g. a PIM (Product Information System) then you must change the product data for each scope manually. That takes time and triggers subtle errors.

Pretty weird but not really solvable to avoid duplicated language specific content and prices in the database.

Suggested new hierarchy

During programming another e-commerce project, lets call it “Project CS”, in a different language, I thought that this can be fixed. But with a refactoring of the database schema this leads mostly to a backwards incompatible break. But I think this seems worth it as it gains much more flexibility.

First of all a scope (int8) can not only be Default, Website, Group or Store but also other values up to 255. The related scope ID (int24) can grow to values up to 8.388.607. This means I can have 8.3m stores in one scope. So the configuration service of “Project CS” can handle all kind of scopes. This removes the above shown limits when configuring settings.

Excursus: Why int8 and int24? Because in “Project CS” I can store the scope (int8) and its related ID (int24) in a single int32 type via bit shifting. For now this is enough, can be optimized later.

The following three print screen show the new structure. A language binds to the website, a country to the group (which means each country can have a different category tree) and the final store consists of the country and language name. Heck it’s even possible to include e.g. a B2B store in Germany. Abbreviation in the print screens: POS = Point of Sales.

Table Website

Website Database Table

Table Group

Group Database Table

Table Store

Store Database Table

The EAV tables must be refactored. An EAV type table must be able to store all scopes with all its IDs. This can be achieved by either adding two new columns for the scope and its scope_id or a single column scope_type_id which merges via bit shifting the scope and the ID. But as humans usually create SQL statements on the fly, it might be better to add two columns. That allows you to create queries without any helper functions to merge/explode scope and ID.

scope column contains either Default (0), Website (1), Group (2) or Store (3) (or as mentioned above values up to 255). Remember hierarchy says: Default->Website->Group->Store, where Store gives the lowest and most granular level.

scope_id column contains the corresponding integer value for the scopes Website, Group and Store. The Default scope always has a zero scope_id.

scope_type_id Example
SELECT 'website'                AS scope_name, 
       1                        AS scope, 
       website_id               AS scope_id, 
       ( 1 << 24 | website_id ) AS scope_type_id, 
       name 
FROM   store_website 
UNION ALL 
SELECT 'group'                AS scope_name, 
       2                      AS scope, 
       group_id               AS scope_id, 
       ( 2 << 24 | group_id ) AS scope_type_id, 
       name 
FROM   store_group 
UNION ALL 
SELECT 'store'                AS scope_name, 
       3                      AS scope, 
       store_id               AS scope_id, 
       ( 3 << 24 | store_id ) AS scope_type_id, 
       name 
FROM   `store` 
ORDER  BY scope_type_id 

Scope Type ID

New simplified catalog product EAV schema

New EAV Table Type Schema

SQL queries for returning a value in the store scope gets more hard.

I’ll give it a try. The following variables apply:

  • attribute ID 83 contains the manufacturer (string)
  • scope 0 = Default
  • scope 1 = Website
  • scope 2 = Group
  • scope 3 = Store
  • scope_id 10 = English (DB table store_website)
  • scope_id 20 = Germany (DB table store_group)
  • scope_id 30 = German store with english language (DB table store)

The scope_id usually starts in all 3 tables with 1 (auto increment) but we want to avoid here confusion ;-).

SELECT cpe.*,
  IFNULL(manufacturerStore.value, 
    IFNULL(manufacturerGroup.value, 
      IFNULL(manufacturerWebsite.value,
        IFNULL(manufacturerDefault.value,'')))) AS `manufacturer`
  FROM
    catalog_product_entity AS `cpe`
    LEFT JOIN catalog_product_entity_varchar AS `manufacturerDefault` 
      ON cpe.entity_id=manufacturerDefault.entity_id AND 
          manufacturerDefault.scope=0 AND manufacturerDefault.scope_id=0 AND 
          manufacturerDefault.attribute_id=83 AND manufacturerDefault.value IS NOT NULL 
    LEFT JOIN catalog_product_entity_varchar AS `manufacturerWebsite` 
      ON cpe.entity_id=manufacturerWebsite.entity_id AND 
          manufacturerWebsite.scope=1 AND manufacturerWebsite.scope_id=10 AND 
          manufacturerWebsite.attribute_id=83 AND manufacturerWebsite.value IS NOT NULL 
    LEFT JOIN catalog_product_entity_varchar AS `manufacturerGroup` 
      ON cpe.entity_id=manufacturerGroup.entity_id AND 
          manufacturerGroup.scope=2 AND manufacturerGroup.scope_id=20 AND 
          manufacturerGroup.attribute_id=83 AND manufacturerGroup.value IS NOT NULL 
    LEFT JOIN catalog_product_entity_varchar AS `manufacturerStore` 
      ON cpe.entity_id=manufacturerStore.entity_id AND 
          manufacturerStore.scope=3 AND manufacturerStore.scope_id=30 AND 
          manufacturerStore.attribute_id=83 AND manufacturerStore.value IS NOT NULL

As you can see we generated a lot of SQL just for selecting one single attribute, but we have the full hierarchy implemented. Now imagine we have 1000 attributes … ;-)

We need to consider the full fallback hierarchy (up to a level of 255 but for now only 4 levels). Each column NULL value falls back to the next scope: Store->Website->Group->Default. But this can be solved by great tools or a generated SQL view or a materialized view or … ;-)

The amount of views or materialized views depends on the amount of stores.

Any more ideas for a database schema? Flat tables would be an option to create for each scope a table. One table contains all columns but I think concurrent row updates will block as row locks leads to blocking.

Schemaless is not an option as I strive for a mathematical correct strict model.

What about prices?

Prices are by Default-Magento bound to the website scope. This needs to be refactored the same way as the EAV tables to remove the website_id column and replace it with the two new columns scope and scope_id (same with sales rules).

As price calculation throws a lot of complexity into the whole system I consider that a dedicated plugable “microservice”, a price engine. Here you throw in scope, scope_id, customer groups, customer IDs, promotion ID, etc and the product ID to retrieve the correct price/s.

What about customers?

Customers are by Default-Magento bound to the website scope. This needs to be refactored the same way as the EAV tables to remove the website_id column and replace it with the two new columns scope andm scope_id. The higher a customer has been assigned to a scope the more s/he can switch between the different scopes.

What about the stock?

Stock levels and warehouses are by Default-Magento bound to the website scope. The table cataloginventory_stock_item has even totally wrong foreign keys which annoys lots of developers ;-). This needs to be refactored the same way as the EAV tables to remove the website_id column and replace it with the two new columns scope and scope_id. The stock can maybe have a configurable fall back to the different scopes but can be also bound to just one specific scope with its ID.

The above change allows us to implement e.g. a “Click & Collect” feature for a merchant with many brick and mortar stores, each with their own stock level.

You can think here also of a dedicated plugable “microservice”.

What about orders?

No changes here as they are still bound to the scope store.

Indexation must be huge!

Project “CS” uses a parallel and concurrent indexer which works totally different than the indexer you know from Default-Magento. This indexer is neither visible to the frontend nor to the backend.

But …

The question remains: Breaking compatibility to Magento? Gaining more flexibility but harder and complex SQL queries? What about MySQL/MariaDB performance?

What do you think?

Write me a comment here, a tweet or an email!

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