# Function

A `Function` instance for generating vector embeddings from user-provided raw data in Milvus.

```java
io.milvus.v2.service.collection.request.CreateCollectionReq.Function
```

## Constructor

This constructor initializes a new `Function` instance designed to transform user's raw data into vector embeddings. This is achieved through an automated process that simplifies similarity search operations.

```java
CreateCollectionReq.Function.builder()
    .name(String name)
    .description(String description)
    .functionType(FunctionType functionType)
    .inputFieldNames(List<String> inputFieldNames)
    .outputFieldNames(List<String> outputFieldNames)
    .params(Map<String, String> params)
    .build()
```

**BUILDER METHODS:**

- `name(String name)`

    The name of the function. This identifier is used to reference the function within queries and collections.

- `description(String description)`

    A brief description of the function's purpose. This can be useful for documentation or clarity in larger projects and defaults to an empty string.

- `functionType(FunctionType functionType)`

    The type of function for processing raw data. Possible values:

    - `FunctionType.BM25`: Uses the BM25 algorithm for generating sparse embeddings from a `VARCHAR` field.

- `inputFieldNames(List<String> inputFieldNames)`

    The name of the field containing the raw data that requires conversion to vector representation. For functions using `FunctionType.BM25`, this parameter accepts only one field name.

- `outputFieldNames(List<String> outputFieldNames)`

    The name of the field where the generated embeddings will be stored. This should correspond to a vector field defined in the collection schema. For functions using `FunctionType.BM25`, this parameter accepts only one field name.

- `params(Map<String, String> params)`

    A set of key-value pairs that configures the function properties.

**RETURN TYPE:**

*Function*

**RETURNS:**

A `Function` object that can be registered with a Milvus collection, facilitating automatic embedding generation during data insertion.

**EXCEPTIONS:**

- **MilvusClientExceptions**

    This exception will be raised when any error occurs during this operation.

## Example

```java
import io.milvus.common.clientenum.FunctionType;
import io.milvus.v2.service.collection.request.CreateCollectionReq.Function;

import java.util.Collections;

CreateCollectionReq.Function.builder()
    .functionType(FunctionType.BM25)
    .name("text_bm25_emb")
    .inputFieldNames(Collections.singletonList("text"))
    .outputFieldNames(Collections.singletonList("vector"))
    .build());
```