4.4.1 Defining users and their inventory

We’ll start by showing some structures that define our users and their inventory. User information is stored as a HASH, with keys and values that store user attributes like name, funds, and anything else. A user’s inventory will be a SET that holds unique identifiers for each item, which can be seen in figure 4.2.

Figure 4.2Example user inventory and user information. Frank has 43 e-dollars and an item that he’s considering selling from his inventory.

Our requirements for the market are simple: a user can list an item for a given price, and when another user purchases the item, the seller receives the money. We’ll also say that the part of the market we’ll be worrying about only needs to be ordered by selling price. In chapter 7, we’ll cover some topics for handling other orders.

Figure 4.3Our basic marketplace that includes an ItemA being sold by user 4 for 35 e-dollars

To include enough information to sell a given item in the market, we’ll concatenate the item ID for the item with the user ID of the seller and use that as a member of a market ZSET, with the score being the item’s selling price. By including all of this information together, we greatly simplify our data structures and what we need to look up, and get the benefit of being able to easily paginate through a presorted market. A small version of the marketplace is shown in figure 4.3.

Now that we know what structures our marketplace uses, let’s list items in the market.