Create Pre README.md

Author: ChandBasha-code

Specialized Areas/ITOM/Discovery/Pre README.md

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+# ServiceNow Discovery Pre Sensor Script: IP Router Association
+
+This script is a **ServiceNow Discovery Pre Sensor Script** designed to enrich discovery payload data before it reaches the **Identification and Reconciliation Engine (IRE)**.  
+
+It focuses on linking **Interface Cards (`cmdb_ci_interface_card`)** to their parent **IP Routers (`cmdb_ci_ip_router`)** by resolving the router name to its corresponding `sys_id` in the CMDB.
+
+
+## Overview
+
+When ServiceNow Discovery runs a pattern that identifies multiple components (e.g., routers and their interface cards), some payload items may contain **router names instead of sys_ids**.  
+The IRE requires sys_ids for accurate relationship building.  
+
+This script ensures that:
+- The `u_configuration_item` field on interface cards is replaced with the actual `sys_id` of the corresponding router.
+- The router’s `managed_by_group` field is also copied to the interface card record.
+- Payload is properly formatted and ready for IRE ingestion.
+
+##  Script Logic
+
+### Step-by-step Flow
+1. **Parse Payload:**  
+   Converts the input payload JSON string into an object for processing.
+
+2. **Iterate Items:**  
+   Loops through each payload item and filters those with `className = cmdb_ci_interface_card`.
+
+3. **Router Resolution:**  
+   For each interface card:
+   - Reads the router name from `u_configuration_item`.
+   - Searches for a matching router record in `cmdb_ci_ip_router`.
+   - If found:
+     - Replaces the router name with its `sys_id`.
+     - Copies the router’s `managed_by_group` value.
+
+4. **Return Updated Payload:**  
+   Returns the modified payload back to Discovery for further processing by the IRE.
+
+---
+
+##  Example Behavior
+
+### **Before Script Execution**
+```json
+{
+  "items": [
+    {
+      "className": "cmdb_ci_interface_card",
+      "values": {
+        "name": "Router-1/Gigabit0/1",
+        "u_configuration_item": "Router-1"
+      }
+    }
+  ]
+}
+
+### **After Script Execution**
+{
+  "items": [
+    {
+      "className": "cmdb_ci_interface_card",
+      "values": {
+        "name": "Router-1/Gigabit0/1",
+        "u_configuration_item": "1b23cdef6f3123006a12ff3b8b3ee490",
+        "managed_by_group": "287ebd7da9fe198100f92cc8d1d2154e"
+      }
+    }
+  ]
+}
+