How to setup ElasticSearch index structure with mu

recently I started working on ElasticSearch (ES) implementation into legacy e-commerce app written in PHP using MySQL. I am completely new to all this stuff and reading the docs is fine, yet I really need somebody with experience to advise me.

From the ES documentation I was able to setup a new cluster and I also found out that rivers are deprecated and should be replaced, so I replaced them with Logstash and JDBC MySQL connector.

At this point I have:

ElasticSearch
Logstash
JDBC MySQL driver
MySQL server

The database structure of the application is not really optimal and is very hard to replace, but I'd like to replicate it into the ES index in the best possible way.

DB Structure:

Products

+-------------------------------+-------+--------+
|              Id               | Title | Price  |
+-------------------------------+-------+--------+
| 00c8234d71c4e94f725cd432ebc04 | Alpha | 589,00 |
| 018357657529fef056cf396626812 | Beta  | 355,00 |
| 01a2c32ceeff0fc6b7dd4fc4302ab | Gamma | 0,00   |
+-------------------------------+-------+--------+

Flags

+------------+-------------+
|     Id     |    Title    |
+------------+-------------+
| sellout    | Sellout     |
| discount   | Discount    |
| topproduct | Top Product |
+------------+-------------+

flagsProducts (n:m pivot)

+------+-------------------------------+------------+------------+
|  Id  |           ProductId           |   FlagId   | ExternalId |
+------+-------------------------------+------------+------------+
| 1552 | 00c8234d71c4e94f725cd432ebc04 | sellout    | NULL       |
| 2845 | 00c8234d71c4e94f725cd432ebc04 | topproduct | NULL       |
| 9689 | 018357657529fef056cf396626812 | discount   | NULL       |
| 4841 | 01a2c32ceeff0fc6b7dd4fc4302ab | discount   | NULL       |
+------+-------------------------------+------------+------------+

Those string IDs are a complete disaster (but I have to deal with them now). At first I thought I should do a flat structure of Products index to ES, but what about multiple entity bindings?

That's a great start!

I would definitely flatten it all out (i.e. denormalize) and come up with product documents that look like the one below. That way you get rid of the N:M relationship between products and flags by simply creating a flags array for each product. It will thus be easier to query those flags.

{
   "id": "00c8234d71c4e94f725cd432ebc04",
   "title": "Alpha",
   "price": 589.0,
   "flags": ["Sellout", "Top Product"]
}
{
   "id": "018357657529fef056cf396626812",
   "title": "Beta",
   "price": 355.0,
   "flags": ["Discount"]
}
{
   "id": "01a2c32ceeff0fc6b7dd4fc4302ab",
   "title": "Gamma",
   "price": 0.0,
   "flags": ["Discount"]
}

The product mapping type would look like this:

PUT products
{
    "mappings": {
        "product": {
            "properties": {
                "id": {
                    "type": "string",
                    "index": "not_analyzed"
                },
                "title": {
                    "type": "string"
                },
                "price": {
                    "type": "double",
                    "null_value": 0.0
                },
                "flags": {
                    "type": "string",
                    "index": "not_analyzed"
                }
            }
        }
    }
}

Since you have the logstash jdbc input already, all you're missing is the proper SQL query to fetch the products and associated flags.

  SELECT p.Id as id, p.Title as title, p.Price as price, GROUP_CONCAT(f.Title) as flags
    FROM Products p
    JOIN flagsProducts fp ON fp.ProductId = p.Id
    JOIN Flags f ON fp.FlagId = f.id
GROUP BY p.Id

Which would get you rows like these:

+-------------------------------+-------+-------+---------------------+
| id                            | title | price | flags               |
+-------------------------------+-------+-------+---------------------+
| 00c8234d71c4e94f725cd432ebc04 | Alpha |   589 | Sellout,Top product |
| 018357657529fef056cf396626812 | Beta  |   355 | Discount            |
| 01a2c32ceeff0fc6b7dd4fc4302ab | Gamma |     0 | Discount            |
+-------------------------------+-------+-------+---------------------+

Using Logstash filters you can then split the flags into an array and you're good to go.