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Javascript – MongoDB container init script which opens file from disk

I’m writing an init script (e.g. /docker-entrypoint-initdb.d/init.js) which will be executed by the mongo Docker image when the container is first created. (See the docs for the image, "Initializing a fresh instance" section.)

Within this script, I need to open a file from disk (on the container), and then insert an object into the database with that file’s content as a property. Something like this:

import fs from "fs";

let data = fs.readFileSync("/path/to/somefile.txt", { encoding: "base64" });

db.example.files.insertOne({
  filename: "somefile.txt",
  data: Binary.createFromBase64(data),
});

But this script is written for NodeJS — how can I do the same in a plain JS script executed via MongoDB directly (e.g. mongosh -f init.js)?

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2

Answers


  1. 0

    Your init.js script, with some minor changes, will work in MongoDB 6.0.15 & 7.0.9. Probably since the NodeJS environment is available during startup.

    TL;DR: Remove the fs import.

    Changes needed:

    1. All the files, including somefile.txt, need to be mounted/linked in docker-compose volumes
    2. The fs import is should be removed 🤔
      • It throws an error and the service doesn’t come up:
      • TypeError: Cannot assign to read only property 'message' of object 'SyntaxError: 'import' and 'export' may appear only with 'sourceType: "module"' (1:0)
    3. Specify the DB with getSiblingDB, otherwise it goes under the test and the collection name becomes example.files; unless that’s what you wanted.

    docker-compose.yml

    services:
  mongo:
    image: mongo:6  # also works with 7
    # image: mongodb/mongodb-community-server:7.0-ubuntu2204  # also works
    volumes:
      - ./db:/data/db
      - ./init.js:/docker-entrypoint-initdb.d/init.js:ro
      - ./somefile.txt:/docker-entrypoint-initdb.d/somefile.txt:ro
    environment:
      MONGO_INITDB_ROOT_USERNAME: root
      MONGO_INITDB_ROOT_PASSWORD: example
    ports:
      - "27017:27017"

    init.js

    let data = fs.readFileSync("./docker-entrypoint-initdb.d/somefile.txt", { encoding: "base64" });

db.getSiblingDB("example").files.insertOne({
  filename: "somefile.txt",
  data: Binary.createFromBase64(data),
});

    Contents of somefile.txt:

    text in somefile

    Result in the DB after first startup:

    loaded record in the DB

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  2. 0

    For MongoDB 5.x and 4.x, this needs to be done in a Shell script, instead of JS. And you’ll need to use BinData with subtype 0, instead of Binary.createFromBase64. The final result is the same in the DB.

    docker-compose.yml

    services:
  mongo:
    image: mongo:5  # also works with 4.4, 4.2, 4.0
    # image: mongodb/mongodb-community-server:4.4.0-ubuntu2004  # also works
    volumes:
      - ./db:/data/db
      - ./init.sh:/docker-entrypoint-initdb.d/init.sh:ro
      - ./somefile.txt:/docker-entrypoint-initdb.d/somefile.txt:ro
    environment:
      MONGO_INITDB_ROOT_USERNAME: root
      MONGO_INITDB_ROOT_PASSWORD: example
    ports:
      - "27017:27017"

    init.sh for MongoDB 5.x

    INIT_BASE64_DATA=$(cat ./docker-entrypoint-initdb.d/somefile.txt | base64)

mongosh admin <<EOF
    use example
    db.files.insertOne({ 
      filename: "somefile.txt", 
      data: BinData(0, "$INIT_BASE64_DATA") 
    });
EOF

    init.sh for MongoDB 4.x, change the mongosh to mongo:

    INIT_BASE64_DATA=$(cat ./docker-entrypoint-initdb.d/somefile.txt | base64)

mongo admin <<EOF
    use example
    db.files.insertOne({ 
      filename: "somefile.txt", 
      data: BinData(0, "$INIT_BASE64_DATA") 
    });
EOF

    Contents of somefile.txt:

    text in somefile

    Result in the DB after first startup:

    loaded record in the DB

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