# Use advanced mapping features
<a name="ddb-en-client-adv-features"></a>

Learn about advanced table schema features in the DynamoDB Enhanced Client API.

## Understand table schema types
<a name="ddb-en-client-adv-features-schm-overview"></a>

`[TableSchema](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/enhanced/dynamodb/TableSchema.html)` is the interface to the mapping functionality of the DynamoDB Enhanced Client API. It can map a data object to and from a map of [AttributeValues](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/dynamodb/model/AttributeValue.html). A `TableSchema` object needs to know about the structure of the table it is mapping. This structure information is stored in a [https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/enhanced/dynamodb/TableMetadata.html](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/enhanced/dynamodb/TableMetadata.html) object.

The enhanced client API has several implementations of `TableSchema`, which follow. 

### Table schema generated from annotated classes
<a name="ddb-en-client-adv-features-schema-mapped"></a>

It is a moderately expensive operation to build a `TableSchema` from annotated classes, so we recommend doing this once, at application startup.

 [ BeanTableSchema ](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/enhanced/dynamodb/mapper/BeanTableSchema.html)   
This implementation is built based on attributes and annotations of a bean class. An example of this approach is demonstrated in the [Get started section](ddb-en-client-gs-tableschema.md#ddb-en-client-gs-tableschema-anno-bean).  
If a `BeanTableSchema` is not behaving as you expect, enable debug logging for `software.amazon.awssdk.enhanced.dynamodb.beans`.

[ImmutableTableSchema](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/enhanced/dynamodb/mapper/ImmutableTableSchema.html)  
This implementation is built from an immutable data class. This approach is described in the [Work with immutable data classes](ddb-en-client-use-immut.md) section.

### Table schema generated with a builder
<a name="ddb-en-client-adv-features-schema-static"></a>

The following `TableSchema`s are built from code by using a builder. This approach is less costly than the approach that uses annotated data classes. The builder approach avoids the use of annotations and doesn't require JavaBean naming standards.

[StaticTableSchema](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticTableSchema.html)  
This implementation is built for mutable data classes. The getting started section of this guide demonstrated how to [generate a `StaticTableSchema` using a builder](ddb-en-client-gs-tableschema.md#ddb-en-client-gs-tableschema-builder).

[StaticImmutableTableSchema](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchema.html)  
Similarly to how you build a `StaticTableSchema`, you generate an implementation of this type of `TableSchema` using a [builder](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchema.html) for use with immutable data classes.

### Table schema for data without a fixed schema
<a name="ddb-en-client-adv-features-schema-document"></a>

[DocumentTableSchema](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/enhanced/dynamodb/document/DocumentTableSchema.html)  
Unlike other implementations of `TableSchema`, you don't define attributes for a `DocumentTableSchema` instance. Usually, you specify only primary keys and attribute converter providers. An `EnhancedDocument` instance provides the attributes that you build from individual elements or from a JSON string.