Let's break down your two MongoDB questions and fix that query issue you're facing:

1. Finding ObjectIds Used as Foreign Keys #

First, let's cover the two common scenarios for how ObjectIds are stored as foreign keys:

Scenario 1: ObjectId is stored as MongoDB's native ObjectId type #

If your foreign key fields use the actual ObjectId type (not a plain string), wrap the value in ObjectId() for an exact match:

// Query a single collection for docs with a top-level foreign key match
db.your_collection.find({ foreign_key_field: ObjectId("6299b9f00f09ff045cc15d") })

// For nested array fields like your sample structure
db.test.find({ "fourk_runs.Objectid": ObjectId("6299b9f00f09ff045cc15d") })

Scenario 2: ObjectId is stored as a string #

If your data stores ObjectIds as plain strings (like the example you shared), use a direct string match without the ObjectId() wrapper:

// Match nested array elements with the string-formatted ObjectId
db.test.find({ "fourk_runs.Objectid": "6299b9f00f09ff045cc15d" })

2. Searching for an ObjectId Across All Fields & Collections in a Database #

Your original $text query didn't work for two key reasons:

• $text searches depend on text indexes created on specific fields — it won't scan unindexed fields automatically.
• Text search uses tokenization, so short ObjectId fragments often don't get matched as expected.

Here are two reliable ways to search every field in every collection for your target ObjectId:

Option 1: Shell Script for Small Databases (Simple Approach) #

Use a MongoDB Shell script to loop through all collections, then recursively check every field and array element for your target value.

For string-formatted ObjectIds:

// Replace with your target ObjectId string
const targetId = "6299b9f00f09ff045cc15d";

// Get all collections in the current database
const collections = db.getCollectionNames();

collections.forEach(colName => {
  const col = db.getCollection(colName);
  // Use $where to recursively scan all fields
  const matches = col.find({
    $where: function() {
      function scanValue(val) {
        // Check if current value is the target string
        if (typeof val === "string" && val === targetId) return true;
        // Check arrays by scanning each element
        if (Array.isArray(val)) return val.some(item => scanValue(item));
        // Check nested objects by scanning their values
        if (typeof val === "object" && val !== null) {
          return Object.values(val).some(nestedVal => scanValue(nestedVal));
        }
        return false;
      }
      return scanValue(this);
    }
  }).toArray();

  if (matches.length > 0) {
    print(`Found ${matches.length} matches in collection: ${colName}`);
    printjson(matches);
  }
});

For native ObjectId type values:

Adjust the script to check for ObjectId instances instead of strings:

const targetId = ObjectId("6299b9f00f09ff045cc15d");

// ... (same collection loop as above)

const matches = col.find({
  $where: function() {
    function scanValue(val) {
      if (val instanceof ObjectId && val.equals(targetId)) return true;
      if (Array.isArray(val)) return val.some(item => scanValue(item));
      if (typeof val === "object" && val !== null) {
        return Object.values(val).some(nestedVal => scanValue(nestedVal));
      }
      return false;
    }
    return scanValue(this);
  }
}).toArray();

Option 2: Optimized Approach for Large Databases #

The $where method can be slow on big datasets. If you know common field names used for ObjectId references (like Objectid, refId, parentId), query those fields directly across collections for better performance:

const targetId = "6299b9f00f09ff045cc15d";
const collections = db.getCollectionNames();

collections.forEach(colName => {
  const col = db.getCollection(colName);
  const matches = col.find({
    $or: [
      { "fourk_runs.Objectid": targetId },
      { "fourk_pass_fail.Objectid": targetId },
      { "dr_runs.Objectid": targetId },
      // Add any other known reference fields here
    ]
  }).toArray();

  if (matches.length > 0) {
    print(`Found ${matches.length} matches in collection: ${colName}`);
    printjson(matches);
  }
});

内容的提问来源于stack exchange，提问作者f.kermani