mongodb-js · jcobis · Oct 8, 2025 · Oct 8, 2025 · Oct 8, 2025 · Oct 8, 2025
@@ -31,6 +31,7 @@ import RawSchemaConfirmationScreen from './raw-schema-confirmation-screen';
 import FakerSchemaEditorScreen from './faker-schema-editor-screen';
 import ScriptScreen from './script-screen';
 import DocumentCountScreen from './document-count-screen';
+import PreviewScreen from './preview-screen';
 
 const footerStyles = css`
   flex-direction: row;
@@ -95,7 +96,15 @@ const MockDataGeneratorModal = ({
           />
         );
       case MockDataGeneratorStep.PREVIEW_DATA:
-        return <></>; // TODO: CLOUDP-333857
+        return (
+          <PreviewScreen
+            confirmedFakerSchema={
+              fakerSchemaGenerationState.status === 'completed'
+                ? fakerSchemaGenerationState.fakerSchema
+                : {}
+            }
+          />
+        );
       case MockDataGeneratorStep.GENERATE_DATA:
         return <ScriptScreen />;
     }

@@ -0,0 +1,43 @@
+import React, { useMemo } from 'react';
+import { css, spacing, Body, Code } from '@mongodb-js/compass-components';
+import { EJSON } from 'bson';
+import type { FakerSchema } from './types';
+import { generateDocument } from './script-generation-utils';
+
+const descriptionStyles = css({
+  marginBottom: spacing[200],
+});
+
+interface PreviewScreenProps {
+  confirmedFakerSchema: FakerSchema;
+}
+
+const NUM_SAMPLE_DOCUMENTS = 3;
+
+function PreviewScreen({ confirmedFakerSchema }: PreviewScreenProps) {
+  const sampleDocuments = useMemo(() => {
+    const documents = [];
+    for (let i = 0; i < NUM_SAMPLE_DOCUMENTS; i++) {
+      documents.push(generateDocument(confirmedFakerSchema));
+    }
+
+    return documents;
+  }, [confirmedFakerSchema]);
+
+  return (
+    <div data-testid="preview-screen">
+      <Body as="h2" baseFontSize={16} weight="medium">
+        Preview Mock Data
+      </Body>
+      <Body className={descriptionStyles}>
+        Below is a sample of documents that will be generated based on your
+        script
+      </Body>
+      <Code language="javascript" copyable={false}>
+        {EJSON.stringify(sampleDocuments, undefined, 2)}
+      </Code>
+    </div>
+  );
+}
+
+export default PreviewScreen;
@@ -1,6 +1,6 @@
 import { expect } from 'chai';
 import { faker } from '@faker-js/faker/locale/en';
-import { generateScript } from './script-generation-utils';
+import { generateScript, generateDocument } from './script-generation-utils';
 import type { FakerFieldMapping } from './types';
 
 /**
@@ -1421,4 +1421,151 @@ describe('Script Generation', () => {
       }
     });
   });
+
+  describe('generateDocument', () => {
+    it('should generate document with simple flat fields', () => {
+      const schema = {
+        name: {
+          mongoType: 'String' as const,
+          fakerMethod: 'person.fullName',
+          fakerArgs: [],
+          probability: 1.0,
+        },
+        age: {
+          mongoType: 'Number' as const,
+          fakerMethod: 'number.int',
+          fakerArgs: [{ json: '{"min": 18, "max": 65}' }],
+          probability: 1.0,
+        },
+      };
+
+      const document = generateDocument(schema);
+
+      expect(document).to.be.an('object');
+      expect(document).to.have.property('name');
+      expect(document.name).to.be.a('string').and.not.be.empty;
+      expect(document).to.have.property('age');
+      expect(document.age).to.be.a('number');
+      expect(document.age).to.be.at.least(18).and.at.most(65);
+    });
+
+    it('should generate document with arrays', () => {
+      const schema = {
+        'tags[]': {
+          mongoType: 'String' as const,
+          fakerMethod: 'lorem.word',
+          fakerArgs: [],
+          probability: 1.0,
+        },
+      };
+
+      const document = generateDocument(schema, { 'tags[]': 2 });
+
+      expect(document).to.be.an('object');
+      expect(document).to.have.property('tags');
+      expect(document.tags).to.be.an('array').with.length(2);
+      for (const tag of document.tags as string[]) {
+        expect(tag).to.be.a('string').and.not.be.empty;
+      }
+    });
+
+    it('should generate document with complex nested arrays and custom lengths', () => {
+      const schema = {
+        'users[].posts[].tags[]': {
+          mongoType: 'String' as const,
+          fakerMethod: 'lorem.word',
+          fakerArgs: [],
+          probability: 1.0,
+        },
+        'matrix[][]': {
+          mongoType: 'Number' as const,
+          fakerMethod: 'number.int',
+          fakerArgs: [{ json: '{"min": 1, "max": 10}' }],
+          probability: 1.0,
+        },
+      };
+
+      const arrayLengthMap = {
+        'users[]': 2,
+        'users[].posts[]': 3,
+        'users[].posts[].tags[]': 4,
+        'matrix[]': 2,
+        'matrix[][]': 3,
+      };
+
+      const document = generateDocument(schema, arrayLengthMap);
+
+      expect(document).to.be.an('object');
+
+      // Check users array structure
+      expect(document).to.have.property('users');
+      expect(document.users).to.be.an('array').with.length(2);
+
+      // Check nested structure with proper types
+      const users = document.users as Array<{
+        posts: Array<{ tags: string[] }>;
+      }>;
+
+      for (const user of users) {
+        expect(user).to.be.an('object');
+        expect(user).to.have.property('posts');
+        expect(user.posts).to.be.an('array').with.length(3);
+
+        for (const post of user.posts) {
+          expect(post).to.be.an('object');
+          expect(post).to.have.property('tags');
+          expect(post.tags).to.be.an('array').with.length(4);
+
+          for (const tag of post.tags) {
+            expect(tag).to.be.a('string').and.not.be.empty;
+          }
+        }
+      }
+
+      // Check matrix (2D array)
+      expect(document).to.have.property('matrix');
+      expect(document.matrix).to.be.an('array').with.length(2);
+
+      const matrix = document.matrix as number[][];
+      for (const row of matrix) {
+        expect(row).to.be.an('array').with.length(3);
+        for (const cell of row) {
+          expect(cell).to.be.a('number').and.be.at.least(1).and.at.most(10);
+        }
+      }
+    });
+
+    it('should handle probability fields correctly', () => {
+      const schema = {
+        name: {
+          mongoType: 'String' as const,
+          fakerMethod: 'person.fullName',
+          fakerArgs: [],
+          probability: 1.0,
+        },
+        optionalField: {
+          mongoType: 'String' as const,
+          fakerMethod: 'lorem.word',
+          fakerArgs: [],
+          probability: 0.0, // Should never appear
+        },
+        alwaysPresent: {
+          mongoType: 'Number' as const,
+          fakerMethod: 'number.int',
+          fakerArgs: [],
+          probability: 1.0,
+        },
+      };
+
+      const document = generateDocument(schema);
+
+      expect(document).to.be.an('object');
+      expect(document).to.have.property('name');
+      expect(document.name).to.be.a('string').and.not.be.empty;
+      expect(document).to.have.property('alwaysPresent');
+      expect(document.alwaysPresent).to.be.a('number');
+      // optionalField should not be present due to 0.0 probability
+      expect(document).to.not.have.property('optionalField');
+    });
+  });
 });