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tessl/maven-dev-langchain4j--langchain4j-chroma

LangChain4j integration for Chroma embedding store enabling storage, retrieval, and similarity search of vector embeddings with metadata filtering support for both API V1 and V2.

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metadata.mddocs/guides/

Metadata Guide

Comprehensive guide to using metadata with ChromaEmbeddingStore.

Overview

Metadata allows attaching key-value pairs to embeddings for:

  • Filtering during search and removal
  • Storing document attributes
  • Organizing and categorizing content
  • Tracking provenance and versioning

Supported Types

Valid Types

Metadata metadata = new Metadata()
    .put("string_field", "value")           // String
    .put("int_field", 42)                   // Integer
    .put("long_field", 123456789L)          // Long
    .put("float_field", 3.14f)              // Float
    .put("double_field", 3.14159)           // Double
    .put("uuid_field", UUID.randomUUID());  // UUID

Unsupported Types

// NOT SUPPORTED - will cause errors
// metadata.put("bool_field", true);      // Boolean - NOT supported
// metadata.put("array_field", array);    // Arrays - NOT supported
// metadata.put("object_field", object);  // Objects - NOT supported

Boolean Workaround

// Option 1: Use string
Metadata meta1 = new Metadata().put("active", "true");
Filter f1 = metadataKey("active").isEqualTo("true");

// Option 2: Use 0/1
Metadata meta2 = new Metadata().put("active", 1);
Filter f2 = metadataKey("active").isEqualTo(1);

Common Metadata Patterns

Document Metadata

Metadata docMetadata = new Metadata()
    .put("title", "Document Title")
    .put("author", "John Doe")
    .put("created_at", System.currentTimeMillis())
    .put("modified_at", System.currentTimeMillis())
    .put("version", 1)
    .put("document_id", UUID.randomUUID());

Categorization

Metadata categoryMetadata = new Metadata()
    .put("category", "technology")
    .put("subcategory", "machine-learning")
    .put("tags", "ai,ml,embeddings")  // Comma-separated
    .put("difficulty", "intermediate");

Source Tracking

Metadata sourceMetadata = new Metadata()
    .put("source", "/docs/guide.pdf")
    .put("page", 42)
    .put("chapter", 3)
    .put("url", "https://example.com/docs/guide.pdf");

Temporal Information

long now = System.currentTimeMillis();
long thirtyDaysAgo = now - (30L * 24 * 60 * 60 * 1000);

Metadata timeMetadata = new Metadata()
    .put("indexed_at", now)
    .put("published_at", thirtyDaysAgo)
    .put("year", 2024)
    .put("month", 3);

Status and Lifecycle

Metadata statusMetadata = new Metadata()
    .put("status", "published")
    .put("visibility", "public")
    .put("archived", 0)  // Boolean as int
    .put("priority", 5);

Quality and Metrics

Metadata qualityMetadata = new Metadata()
    .put("rating", 4.5)
    .put("views", 1250)
    .put("likes", 87)
    .put("confidence", 0.95);

Creating Metadata

Empty Metadata

Metadata meta = new Metadata();

With Initial Values

Metadata meta = new Metadata()
    .put("key1", "value1")
    .put("key2", 42)
    .put("key3", 3.14);

From Map

Map<String, Object> map = new HashMap<>();
map.put("author", "John Doe");
map.put("year", 2024);
map.put("rating", 4.5);

Metadata meta = new Metadata(map);

Builder Pattern

public class MetadataBuilder {

    public static Metadata forDocument(
        String author,
        int year,
        String category
    ) {
        return new Metadata()
            .put("author", author)
            .put("year", year)
            .put("category", category)
            .put("indexed_at", System.currentTimeMillis());
    }
}

// Usage
Metadata meta = MetadataBuilder.forDocument("John Doe", 2024, "tech");

Reading Metadata

Type-Specific Getters

Metadata meta = segment.metadata();

String author = meta.getString("author");
Integer year = meta.getInteger("year");
Double rating = meta.getDouble("rating");
UUID id = meta.getUUID("document_id");
Long timestamp = meta.getLong("created_at");
Float score = meta.getFloat("score");

Safe Reading with Defaults

// Check existence first
if (meta.containsKey("year")) {
    int year = meta.getInteger("year");
}

// Or handle null
Integer year = meta.getInteger("year");
if (year != null) {
    // Use year
} else {
    // Use default
    year = 2024;
}

Converting to Map

Map<String, Object> map = meta.toMap();

// Iterate all values
for (Map.Entry<String, Object> entry : map.entrySet()) {
    System.out.println(entry.getKey() + ": " + entry.getValue());
}

Filtering by Metadata

Equality Filters

Filter authorFilter = metadataKey("author").isEqualTo("John Doe");
Filter categoryFilter = metadataKey("category").isEqualTo("tech");

Numeric Filters

// Only work with numeric metadata
Filter yearFilter = metadataKey("year").isGreaterThanOrEqualTo(2020);
Filter ratingFilter = metadataKey("rating").isGreaterThan(4.0);
Filter priorityFilter = metadataKey("priority").isLessThanOrEqualTo(5);

Collection Filters

Filter categoriesFilter = metadataKey("category")
    .isIn(Arrays.asList("tech", "science", "engineering"));

Filter excludeStatuses = metadataKey("status")
    .isNotIn(Arrays.asList("draft", "archived"));

See: Filtering Guide for complete filter documentation.

Metadata Schema Design

Planning Your Schema

Consider these questions:

  1. What filtering will you need?
  2. What attributes describe your documents?
  3. How will documents be organized?
  4. What temporal information matters?
  5. What provenance is important?

Example Schema

public class DocumentMetadataSchema {

    public static Metadata create(
        String documentId,
        String source,
        String category,
        String author,
        int year,
        double rating
    ) {
        return new Metadata()
            // Identity
            .put("document_id", UUID.fromString(documentId))
            .put("source", source)

            // Classification
            .put("category", category)
            .put("author", author)

            // Temporal
            .put("year", year)
            .put("indexed_at", System.currentTimeMillis())

            // Quality
            .put("rating", rating)

            // Status
            .put("status", "published")
            .put("version", 1);
    }
}

Consistent Naming

// GOOD: Consistent naming conventions
.put("created_at", timestamp)
.put("updated_at", timestamp)
.put("indexed_at", timestamp)

// BAD: Inconsistent naming
.put("createdAt", timestamp)      // camelCase
.put("updated_time", timestamp)   // Different suffix
.put("indexTimestamp", timestamp) // Different format

Use Standard Fields

public interface StandardMetadataFields {
    String ID = "id";
    String SOURCE = "source";
    String CATEGORY = "category";
    String AUTHOR = "author";
    String CREATED_AT = "created_at";
    String UPDATED_AT = "updated_at";
    String STATUS = "status";
    String VERSION = "version";
}

// Usage
Metadata meta = new Metadata()
    .put(StandardMetadataFields.ID, id)
    .put(StandardMetadataFields.SOURCE, source)
    .put(StandardMetadataFields.CATEGORY, category);

Advanced Patterns

Hierarchical Categories

// Use multiple fields for hierarchy
Metadata hierarchical = new Metadata()
    .put("category_l1", "technology")
    .put("category_l2", "artificial-intelligence")
    .put("category_l3", "machine-learning");

// Filter at any level
Filter l1Filter = metadataKey("category_l1").isEqualTo("technology");
Filter l2Filter = metadataKey("category_l2").isEqualTo("artificial-intelligence");

Versioning

Metadata versionedMetadata = new Metadata()
    .put("document_id", documentId)
    .put("version", 2)
    .put("created_at", originalTimestamp)
    .put("updated_at", System.currentTimeMillis())
    .put("changelog", "Fixed typos, updated examples");

// Query latest version
Filter latestVersion = metadataKey("document_id").isEqualTo(documentId);
// Then sort by version in application code

Multi-Value Fields (Workaround)

Since arrays aren't supported, use comma-separated strings:

// Store
Metadata meta = new Metadata()
    .put("tags", "ai,ml,embeddings,vector-search");

// Parse when needed
String tags = meta.getString("tags");
List<String> tagList = Arrays.asList(tags.split(","));

// Filter (limited - can only match exact string)
Filter tagFilter = metadataKey("tags").isEqualTo("ai,ml,embeddings,vector-search");

// Better: Use separate fields for important multi-values
Metadata betterMeta = new Metadata()
    .put("primary_tag", "ai")
    .put("secondary_tag", "ml")
    .put("tertiary_tag", "embeddings");

Computed Metadata

public Metadata computeMetadata(String text, String source) {
    Metadata meta = new Metadata()
        .put("source", source)
        .put("indexed_at", System.currentTimeMillis());

    // Compute values
    int wordCount = text.split("\\s+").length;
    meta.put("word_count", wordCount);

    // Categorize by length
    String lengthCategory = wordCount < 100 ? "short" :
                           wordCount < 500 ? "medium" : "long";
    meta.put("length_category", lengthCategory);

    // Extract year from text if possible
    Pattern yearPattern = Pattern.compile("\\b(19|20)\\d{2}\\b");
    Matcher matcher = yearPattern.matcher(text);
    if (matcher.find()) {
        meta.put("extracted_year", Integer.parseInt(matcher.group()));
    }

    return meta;
}

Performance Considerations

Keep Metadata Lean

// GOOD: Compact metadata
Metadata compact = new Metadata()
    .put("id", id)
    .put("category", category)
    .put("year", year);

// BAD: Storing large text in metadata
Metadata bloated = new Metadata()
    .put("id", id)
    .put("full_text", longDocument);  // Store in TextSegment instead

Indexable Fields

Choose metadata fields that you'll filter on:

// Fields you'll filter on
Metadata filterable = new Metadata()
    .put("category", "tech")      // Will filter
    .put("year", 2024)            // Will filter
    .put("status", "published");  // Will filter

// Metadata that doesn't need filtering can still be stored
filterable.put("notes", "Internal notes");  // Won't filter, just metadata

Best Practices

  1. Use consistent naming - Stick to one convention (snake_case recommended)
  2. Plan your schema - Think about filtering needs upfront
  3. Use appropriate types - Numeric for comparisons, strings for equality
  4. Keep it lean - Don't store large data in metadata
  5. Document your schema - Help others understand your metadata structure
  6. Use standard fields - Common fields across documents
  7. Version your schema - Include schema version in metadata if it evolves
  8. Validate metadata - Check types and constraints before storing
  9. Test filters - Ensure metadata supports your query patterns
  10. Handle missing values - Always check for null when reading

Validation

Metadata Validator

public class MetadataValidator {

    public void validate(Metadata meta) {
        // Required fields
        if (!meta.containsKey("category")) {
            throw new IllegalArgumentException("category is required");
        }

        // Type validation
        Integer year = meta.getInteger("year");
        if (year != null && (year < 1900 || year > 2100)) {
            throw new IllegalArgumentException("invalid year: " + year);
        }

        // Value validation
        String status = meta.getString("status");
        if (status != null &&
            !Arrays.asList("draft", "published", "archived").contains(status)) {
            throw new IllegalArgumentException("invalid status: " + status);
        }
    }
}

Related

Examples

See:

Install with Tessl CLI

npx tessl i tessl/maven-dev-langchain4j--langchain4j-chroma

docs

guides

batch-operations.md

configuration.md

error-handling.md

filtering.md

metadata.md

migration.md

performance.md

rag-pattern.md

semantic-search.md

index.md

tile.json