LanceDB C API Documentation

Welcome to the LanceDB C API documentation. This library provides C bindings for LanceDB, a developer-friendly, serverless vector database for AI applications.

Contents:

• API Reference
  • Complete API

Overview

The LanceDB C API provides a complete interface to LanceDB functionality including:

• Database connections and configuration

• Table creation and management

• Data insertion and querying

• Vector similarity search

• Index creation and management

Quick Start

This example shows how to create a LanceDB table with vector data using Apache Arrow.

1. Connect to a database:

#include <lancedb.h>
#include <arrow/c/bridge.h>
#include <arrow/api.h>

// Create a connection to a local database
LanceDBConnectBuilder* builder = lancedb_connect("./my_database");
LanceDBConnection* db = lancedb_connect_builder_execute(builder);

2. Create Arrow schema (using Arrow C++ API):

// Define schema with id and vector columns
auto id_field = arrow::field("id", arrow::int32());
auto vector_field = arrow::field("vector",
                                 arrow::fixed_size_list(arrow::float32(), 128));
auto schema = arrow::schema({id_field, vector_field});

// Export to C ABI
struct ArrowSchema c_schema;
arrow::ExportSchema(*schema, &c_schema);

3. Create data (using Arrow builders):

arrow::Int32Builder id_builder;
arrow::FixedSizeListBuilder vector_builder(
    arrow::default_memory_pool(),
    std::make_unique<arrow::FloatBuilder>(),
    128  // dimension
);

// Add 100 rows
for (int i = 0; i < 100; i++) {
    id_builder.Append(i);

    auto* float_builder = static_cast<arrow::FloatBuilder*>(
        vector_builder.value_builder());
    for (int j = 0; j < 128; j++) {
        float_builder->Append(i * 0.1f + j);
    }
    vector_builder.Append();
}

// Build arrays
std::shared_ptr<arrow::Array> id_array, vector_array;
id_builder.Finish(&id_array);
vector_builder.Finish(&vector_array);

// Create RecordBatch
auto batch = arrow::RecordBatch::Make(schema, 100, {id_array, vector_array});

// Export to C ABI
struct ArrowArray c_array;
arrow::ExportRecordBatch(*batch, &c_array, &c_schema);

4. Create table with schema and data:

// Create reader from Arrow C ABI
LanceDBRecordBatchReader* reader = lancedb_record_batch_reader_from_arrow(
    (FFI_ArrowArray*)&c_array,
    (FFI_ArrowSchema*)&c_schema
);

// Create table
LanceDBTable* table;
char* error_message = NULL;

LanceDBError result = lancedb_table_create(
    db,
    "my_vectors",
    (FFI_ArrowSchema*)&c_schema,
    reader,
    &table,
    &error_message
);

if (result == LANCEDB_SUCCESS) {
    printf("Table created with %lu rows\n", lancedb_table_count_rows(table));
    lancedb_table_free(table);
} else {
    fprintf(stderr, "Error: %s\n", error_message);
    lancedb_free_string(error_message);
}

// Clean up
lancedb_connection_free(db);