How can I clone a Mongoose schema for archiving without retaining unique constraints and indexes?

Below is one proven approach: instead of cloning the schema with schema.clone() (which carries over indexes and their options), rebuild a “clean” schema from the original definition. This way you guarantee that no unique constraints or indexes are copied over. Here’s one pattern:

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Steps

1. Extract the Schema Definition Tree

   Mongoose stores the “raw” structure in schema.obj. Use that to rebuild a new schema.

2. Remove the Unique and Index Options

   Recursively traverse the definition object and delete (or disable) any unique or index options. This frees the new schema from having these constraints.

3. Set autoIndex: false

   In the schema constructor options, turn off auto-indexing so that Mongoose won’t re-create indexes on startup.

4. Rebuild the Schema

   Create a new Schema from the cleaned-up definition tree and options.

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Example Implementation

Below is an example in TypeScript:

TYPESCRIPTCopied
import { Schema, SchemaDefinition, SchemaOptions } from 'mongoose';

// A helper function that recursively removes unique/index options from a schema definition.
function cleanSchemaDefinition(definition: SchemaDefinition): SchemaDefinition {
  const cleanedDef: SchemaDefinition = {};

  for (const field in definition) {
    if (!definition.hasOwnProperty(field)) continue;

    let fieldDef: any = definition[field];

    // If the field is an object definition (which may include index/unique settings)
    if (fieldDef && typeof fieldDef === 'object' && !Array.isArray(fieldDef)) {
      // Clone the object to avoid mutating the original
      fieldDef = { ...fieldDef };

      // Remove unique and index options if present.
      if (fieldDef.unique) {
        delete fieldDef.unique;
      }
      if (fieldDef.index) {
        delete fieldDef.index;
      }

      // If the field definition contains a nested schema (like a subdocument)
      if (fieldDef.type === Object && fieldDef.properties) {
        fieldDef.properties = cleanSchemaDefinition(fieldDef.properties);
      } else if (fieldDef.type && fieldDef.type instanceof Schema) {
        // For nested Schema instances, you might want to clean them as well.
        fieldDef.type = createCleanSchema(fieldDef.type).ast; // obtaining the AST if needed
      } else if (fieldDef instanceof Schema) {
        // In case the field itself is a Schema
        fieldDef = createCleanSchema(fieldDef);
      }
    }
    cleanedDef[field] = fieldDef;
  }
  return cleanedDef;
}

// Function that creates a new schema from an existing one without unique constraints and indexes
function createCleanSchema(originalSchema: Schema): Schema {
  // 1. Grab the raw definition
  const rawDefinition = originalSchema.obj as SchemaDefinition;

  // 2. Clean the definition by removing unique/index options
  const cleanedDefinition = cleanSchemaDefinition(rawDefinition);

  // 3. Use the original options, but disable auto-indexing
  const originalOptions: SchemaOptions = { ...(originalSchema.options as SchemaOptions) };
  originalOptions.autoIndex = false;

  // 4. Create and return the new Schema
  return new Schema(cleanedDefinition, originalOptions);
}

// Usage:
const originalSchema = new Schema({
  email: { type: String, unique: true, required: true },
  name: String,
  nested: {
    phone: { type: String, unique: true }
  }
  // ... other fields
});

const archivedSchema = createCleanSchema(originalSchema);

// Optionally, check that there are no indexes
console.log(archivedSchema.indexes());

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Explanation

• Avoiding schema.clone():
  Using schema.clone() copies all underlying index definitions (including unique constraints). Instead, we rebuild the schema via the JSON-like object available as schema.obj. This ensures the new schema starts “clean.”

• Recursive Cleaning:
  The helper function cleanSchemaDefinition traverses each path in the original schema definition and deletes the unique and index options. You can expand this function to handle deeper nested objects or arrays as required by your schema’s structure.

• Disabling autoIndex:
  By setting autoIndex: false in the options, you prevent Mongoose from auto-creating indexes on model initialization. This is useful for archived collections where indexes might not be required.

• Rebuilt Schema:
  The new schema now mirrors the structural layout of the original without carrying over the unique constraints or indexes. This schema can be used to archive documents without conflict.

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This approach ensures you only have the fields and structure from your original schema while stripping away unique indexes automatically defined by Mongoose.