MuleSoft Mastery: From Zero to Hero | Ch.03

<!-- Save the incoming request payload before a DB call -->
<set-variable variableName="requestBody" value="#[payload]"/>

<!-- Target attribute: stash DB result in vars.customer, payload unchanged -->
<db:select config-ref="H2_Config" target="customer">
  <db:sql>SELECT * FROM customers WHERE id = :id</db:sql>
  <db:input-parameters>#[{ id: vars.customerId as Number }]</db:input-parameters>
</db:select>

// ─── PAYLOAD ──────────────────────────────────────────────────
payload                                // entire payload
payload.customerId                     // field inside a JSON object
payload[0]                             // first item of an array
payload.name?                          // safe nav — null if missing, no error
payload.email default "n/a"           // fallback if null

// ─── ATTRIBUTES ───────────────────────────────────────────────
attributes.method                      // "GET", "POST", "PUT"…
attributes.queryParams.search          // ?search=Alice
attributes.uriParams.id                // /customers/{id}
attributes.headers.Authorization       // "Bearer eyJ…"
attributes.headers."Content-Type"     // quotes for hyphenated keys

// ─── VARIABLES ────────────────────────────────────────────────
vars.requestId                         // UUID set at flow start
vars.startTime                         // timestamp for perf logging
vars.customerData                      // DB result via target=

// ─── USEFUL BUILT-INS ─────────────────────────────────────────
now()                                  // current DateTime
uuid()                                 // UUID v4 — perfect for trace IDs
sizeOf(payload)                        // array length or string length
isEmpty(payload)                       // true for empty array/string/null
now() as String {format: "yyyy-MM-dd'T'HH:mm:ss'Z'"}   // ISO 8601
attributes.headers['x-correlation-id'] default uuid()   // trace pattern

%dw 2.0
output application/json
---
payload map (row) -> {
  id:        row.ID,
  name:      row.NAME,
  email:     row.EMAIL,
  createdAt: row.CREATED_AT as String {format: "yyyy-MM-dd"},
  status:    upper(row.STATUS default "active")
}

%dw 2.0
output application/json
var activeOnes = payload filter (row) -> row.ACTIVE == true
---
{
  total:     sizeOf(activeOnes),
  customers: activeOnes orderBy ((row) -> row.NAME)
                        map (row) -> {
                          id:    row.ID,
                          name:  row.NAME,
                          // conditional field — only if phone is not null
                          (phone: row.PHONE) if (row.PHONE != null)
                        }
}

<scatter-gather timeout="5000" doc:name="Customer 360">
  <!-- Route 0 — DB lookup -->
  <route>
    <db:select config-ref="H2_Config">
      <db:sql>SELECT * FROM customers WHERE id = :id</db:sql>
      <db:input-parameters>#[{ id: vars.customerId }]</db:input-parameters>
    </db:select>
  </route>
  <!-- Route 1 — HTTP -->
  <route>
    <http:request config-ref="Order_API" path="/orders"/>
  </route>
  <!-- Route 2 — HTTP -->
  <route>
    <http:request config-ref="Banking_API" path="/balance"/>
  </route>
</scatter-gather>

<!-- Merge results — note the .payload accessor on each route -->
<ee:transform>
  <ee:message>
    <ee:set-payload><![CDATA[%dw 2.0
output application/json
---
{
  customer: payload['0'].payload[0],
  orders:   payload['1'].payload,
  balance:  payload['2'].payload
}]]></ee:set-payload>
  </ee:message>
</ee:transform>

<!-- Try with typed error handlers -->
<try>
  <db:select config-ref="H2_Config">
    <db:sql>SELECT * FROM customers WHERE id = :id</db:sql>
    <db:input-parameters>#[{ id: vars.customerId }]</db:input-parameters>
  </db:select>
  <error-handler>
    <on-error-continue type="DB:CONNECTIVITY">
      <set-variable variableName="httpStatus" value="503"/>
      <logger level="ERROR" message="DB unavailable — returning 503"/>
    </on-error-continue>
  </error-handler>
</try>

<!-- Until-Successful: retry a flaky API up to 3 times, 2s between tries -->
<until-successful maxRetries="3" millisBetweenRetries="2000">
  <http:request config-ref="FlakyPartner_API"
                method="GET" path="/sync"/>
</until-successful>

// src/main/resources/dwl/errorResponse.dwl
// Import: import buildError, buildErrors from dwl::errorResponse

%dw 2.0

fun buildError(statusCode, level, errorCode, description, cause = null, field = null) = {
  status:    statusCode,
  level:     level,
  timestamp: now() as String {format: "yyyy-MM-dd'T'HH:mm:ss'Z'"},
  messages: [{
    errorCode:        errorCode,
    errorDescription: description,
    (cause: cause) if cause != null,
    (field: field) if field != null
  }]
}

fun buildErrors(statusCode, errors) = {
  status:    statusCode,
  level:     "ERROR",
  timestamp: now() as String {format: "yyyy-MM-dd'T'HH:mm:ss'Z'"},
  messages:  errors
}

%dw 2.0
output application/json
import buildError, buildErrors from dwl::errorResponse
---

// 400 — Invalid input format
buildError(400, "ERROR", "INVALID_ID",
  "Customer ID must be a positive integer",
  "Received: '" ++ attributes.uriParams.id ++ "'",
  "uriParams.id")

// 404 — Not found
buildError(404, "ERROR", "CUSTOMER_NOT_FOUND",
  "No customer found with the given identifier",
  "ID '" ++ vars.customerId ++ "' not in customers table",
  "uriParams.id")

// 422 — Multiple validation errors AT ONCE (don't just return the first!)
buildErrors(422, [
  { errorCode: "MISSING_EMAIL",  errorDescription: "Email is required",    field: "body.email" },
  { errorCode: "INVALID_PHONE",  errorDescription: "Invalid phone format", field: "body.phone" }
])

// 503 — Upstream service down
buildError(503, "ERROR", "DB_UNAVAILABLE",
  "Service temporarily unavailable. Please retry shortly.",
  error.description)

// 500 — Catch-all
buildError(500, "ERROR", "INTERNAL_SERVER_ERROR",
  "An unexpected error occurred. Our team has been notified.")

<flow name="get-customer-v2-flow">
  <http:listener config-ref="HTTP_Listener_config"
                 path="/customers/{id}/v2" allowedMethods="GET">
    <http:response statusCode="#[vars.httpStatus default 200]"/>
  </http:listener>

  <!-- Tracing — generate or propagate correlation id -->
  <set-variable variableName="requestId"
                value="#[attributes.headers['x-correlation-id'] default uuid()]"/>
  <set-variable variableName="startTime" value="#[now()]"/>

  <!-- Input validation before DB — no wasted queries -->
  <choice>
    <when expression="#[!(attributes.uriParams.id matches /^[1-9][0-9]*$/)]">
      <set-variable variableName="httpStatus" value="400"/>
      <ee:transform>
        <ee:message>
          <ee:set-payload><![CDATA[%dw 2.0
output application/json
import buildError from dwl::errorResponse
---
buildError(400, "ERROR", "INVALID_ID",
  "Customer ID must be a positive integer",
  "Received: '" ++ attributes.uriParams.id ++ "'",
  "uriParams.id")]]></ee:set-payload>
        </ee:message>
      </ee:transform>
    </when>
    <otherwise>
      <!-- DB call wrapped in try with typed handler -->
      <try>
        <!-- … db:select + choice for found/notfound … -->
        <error-handler>
          <on-error-continue type="DB:CONNECTIVITY">
            <!-- 503 envelope -->
          </on-error-continue>
        </error-handler>
      </try>
    </otherwise>
  </choice>

  <!-- Performance log on every request -->
  <logger level="INFO"
          message="#['[' ++ vars.requestId ++ '] ' ++ (vars.httpStatus default 200) as String ++ ' in ' ++ ((now() - vars.startTime) as String) ++ 'ms']"/>
</flow>