ucast-prisma: add example to README

packages/ucast-prisma/README.md

@@ -9,6 +9,69 @@ This package contains helpers for using ucast conditions with Prisma queries.
 > This is an experimental package and is subject to change.
 
 
+## Usage
+
+This package can be used to add filtering to Prisma queries from ucast conditions.
+
+```diff
+router.get("/tickets", async (req, res) => {
+- const { allow, reason } = await authz.authorized(
++ const { allow, reason, conditions } = await authz.authorized(path, { action: "list" }, req);
+  if (!allow) return res.status(FORBIDDEN).json({ reason });
+
++ const filters = ucastToPrisma(conditions, "tickets");
+  const tickets = (
+    await prisma.tickets.findMany({
+      where: {
+        tenant: req.auth.tenant.id,
++       ...filters,
+      },
+      include: {
+        customers: true,
+        users: true,
+      },
+    })
+    ).map((ticket) => toTicket(ticket));
+  return res.status(OK).json({ tickets });
+});
+```
+
+The conditions returned by the OPA policy evaluation looks like this:
+
+```json
+{
+  "conditions": {
+    "or": [
+      { "tickets.resolved": false },
+      { "users.name": "ceasar" }
+    ]
+  }
+}
+```
+
+and the call to `ucastToPrisma(conditions, "tickets")` turns it into this
+Prisma query:
+
+```json
+{
+  "OR": [
+    {
+      "resolved": {
+        "equals": false
+      }
+    },
+    {
+      "users": {
+        "name": {
+          "equals": "ceasar"
+        }
+      }
+    }
+  ]
+}
+```
+
+
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