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Avrotize is a command-line tool for converting data structure definitions between different schema formats, using Apache Avro Schema as the integration schema model.

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Avrotize

Avrotize is a command-line tool for converting data structure definitions between different schema formats, using Apache Avro Schema as the integration schema model.

You can use the tool to convert between Avro Schema and other schema formats like JSON Schema, XML Schema (XSD), Protocol Buffers (Protobuf), ASN.1, and database schema formats like Kusto Data Table Definition (KQL) and T-SQL Table Definition (SQL). That means you can also convert from JSON Schema to Protobuf going via Avro Schema.

You can also generate C#, Java, TypeScript, JavaScript, and Python code from the Avro Schema documents with Avrotize. The difference to the native Avro tools is that Avrotize can emit data classes without Avro library dependencies and, optionally, with annotations for JSON serialization libraries like Jackson or System.Text.Json.

The tool does not convert data (instances of schemas), only the data structure definitions.

Mind that the primary objective of the tool is the conversion of schemas that describe data structures used in applications, databases, and message systems. While the project's internal tests do cover a lot of ground, it is nevertheless not a primary goal of the tool to convert every complex document schema like those used for devops pipeline or system configuration files.

Why?

Data structure definitions are an essential part of data exchange, serialization, and storage. They define the shape and type of data, and they are foundational for tooling and libraries for working with the data. Nearly all data schema languages are coupled to a specific data exchange or storage format, locking the definitions to that format.

Avrotize is designed as a tool to "unlock" data definitions from JSON Schema or XML Schema and make them usable in other contexts. The intent is also to lay a foundation for transcoding data from one format to another, by translating the schema definitions as accurately as possible into the schema model of the target format's schema. The transcoding of the data itself requires separate tools that are beyond the scope of this project.

The use of the term "data structure definition" and not "data object definition" is quite intentional. The focus of the tool is on data structures that can be used for messaging and eventing payloads, for data serialization, and for database tables, with the goal that those structures can be mapped cleanly from and to common programming language types.

Therefore, Avrotize intentionally ignores common techniques to model object-oriented inheritance. For instance, when converting from JSON Schema, all content from allOf expressions is merged into a single record type rather than trying to model the inheritance tree in Avro.

Why Avro Schema?

Apache Avro Schema is the "pivot point" for this tool. All schemas are converted from and to Avro Schema.

Avro Schema ...

  • provides a simple, clean, and concise way to define data structures. It is quite easy to understand and use.
  • is self-contained by design without having or requiring external references. Avro Schema can express complex data structure hierarchies spanning multiple namespace boundaries all in a single file, which neither JSON Schema nor XML Schema nor Protobuf can do.
  • can be resolved by code generators and other tools "top-down" since it enforces dependencies to be ordered such that no forward-referencing occurs.
  • emerged out of the Apache Hadoop ecosystem and is widely used for serialization and storage of data and for data exchange between systems.
  • supports native and logical types that cover the needs of many business and technical use cases.
  • can describe the popular JSON data encoding very well and in a way that always maps cleanly to a wide range of programming languages and systems. In contrast, it's quite easy to inadvertently define a JSON Schema that is very difficult to map to a programming language structure.
  • is itself expressed as JSON. That makes it easy to parse and generate, which is not the case for Protobuf or ASN.1, which require bespoke parsers.

It needs to be noted here that while Avro Schema is great for defining data structures, and data classes generated from Avro Schema using this tool or other tools can be used to with the most popular JSON serialization libraries, the Apache Avro project's own JSON encoding has fairly grave interoperability issues with common usage of JSON. A alternate Avro JSON encoding that is more interoperable is proposed in avrojson.md for submission to the Apache Avro project; the document also enumerates the specific interoperability issues.

Avro Schema does not support all the bells and whistles of XML Schema or JSON Schema, but that is a feature, not a bug, as it ensures the portability of the schemas across different systems and infrastructures. Specifically, Avro Schema does not support many of the data validation features found in JSON Schema or XML Schema. There are no pattern, format, minimum, maximum, or required keywords in Avro Schema, and Avro does not support conditional validation.

In a system where data originates as XML or JSON described by a validating XML Schema or JSON Schema, the assumption we make here is that data will be validated using its native schema language first, and then the Avro Schema will be used for transformation or transfer or storage.

Adding CloudEvents columns for database tables

When converting Avro Schema to Kusto Data Table Definition (KQL), T-SQL Table Definition (SQL), or Parquet Schema, the tool can add special columns for CloudEvents attributes. CNCF CloudEvents is a specification for describing event data in a common way.

The rationale for adding such columns to database tables is that messages and events commonly separate event metadata from the payload data, while that information is merged when events are projected into a database. The metadata often carries important context information about the event that is not contained in the payload itself. Therefore, the tool can add those columns to the database tables for easy alignment of the message context with the payload when building event stores.

Installation

You can install Avrotize from PyPI, having installed Python 3.11 or later:

pip install avrotize

Usage

Avrotize provides several commands for converting schema formats via Avro Schema.

Converting to Avro Schema:

Converting from Avro Schema:

Generate code from Avro Schema:

Convert Proto schema to Avro schema

avrotize p2a --proto <path_to_proto_file> --avsc <path_to_avro_schema_file>

Parameters:

  • --proto: The path to the Protobuf schema file to be converted.
  • --avsc: The path to the Avro schema file to write the conversion result to.

Conversion notes:

  • Proto 2 and Proto 3 syntax are supported.
  • Proto package names are mapped to Avro namespaces. The tool does resolve imports and consolidates all imported types into a single Avro schema file.
  • The tool embeds all 'well-known' Protobuf 3.0 types in Avro format and injects them as needed when the respective types are imported. Only the Timestamp type is mapped to the Avro logical type 'timestamp-millis'. The rest of the well-known Protobuf types are kept as Avro record types with the same field names and types.
  • Protobuf allows any scalar type as key in a map, Avro does not. When converting from Proto to Avro, the type information for the map keys is ignored.
  • The field numbers in message types are not mapped to the positions of the fields in Avro records. The fields in Avro are ordered as they appear in the Proto schema. Consequently, the Avro schema also ignores the extensions and reserved keywords in the Proto schema.
  • The optional keyword results in an Avro field being nullable (union with the null type), while the required keyword results in a non-nullable field. The repeated keyword results in an Avro field being an array of the field type.
  • The oneof keyword in Proto is mapped to an Avro union type.
  • All options in the Proto schema are ignored.

Convert Avro schema to Proto schema

avrotize a2p --avsc <path_to_avro_schema_file> --proto <path_to_proto_directory>

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --proto: The path to the Protobuf schema directory to write the conversion result to.

Conversion notes:

  • Avro namespaces are resolved into distinct proto package definitions. The tool will create a new .proto file with the package definition and an import statement for each namespace found in the Avro schema.
  • Avro type unions [] are converted to oneof expressions in Proto. Avro allows for maps and arrays in the type union, whereas Proto only supports scalar types and message type references. The tool will therefore emit message types containing a single array or map field for any such case and add it to the containing type, and will also recursively resolve further unions in the array and map values.
  • The sequence of fields in a message follows the sequence of fields in the Avro record. When type unions need to be resolved into oneof expressions, the alternative fields need to be assigned field numbers, which will shift the field numbers for any subsequent fields.

Convert JSON schema to Avro schema

avrotize j2a --jsons <path_to_json_schema_file> --avsc <path_to_avro_schema_file> [--namespace <avro_schema_namespace>]

Parameters:

  • --jsons: The path to the JSON schema file to be converted.
  • --avsc: The path to the Avro schema file to write the conversion result to.
  • --namespace: (optional) The namespace to use in the Avro schema if the JSON schema does not define a namespace.

Conversion notes:

Convert Avro schema to JSON schema

avrotize a2j --avsc <path_to_avro_schema_file> --json <path_to_json_schema_file>

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --json: The path to the JSON schema file to write the conversion result to.

Conversion notes:

Convert XML Schema (XSD) to Avro schema

avrotize x2a --xsd <path_to_xsd_file> --avsc <path_to_avro_schema_file> [--namespace <avro_schema_namespace>]

Parameters:

  • --xsd: The path to the XML schema file to be converted.
  • --avsc: The path to the Avro schema file to write the conversion result to.
  • --namespace: (optional) The namespace to use in the Avro schema if the XML schema does not define a namespace.

Conversion notes:

  • All XML Schema constructs are mapped to Avro record types with fields, whereby both, elements and attributes, become fields in the record. XML is therefore flattened into fields and this aspect of the structure is not preserved.
  • Avro does not support xsd:any as Avro does not support arbitrary typing and must always use a named type. The tool will map xsd:any to a field any typed as a union that allows scalar values or two levels of array and/or map nesting.
  • simpleType declarations that define enums are mapped to enum types in Avro. All other facets are ignored and simple types are mapped to the corresponding Avro type.
  • complexType declarations that have simple content where a base type is augmented with attributes is mapped to a record type in Avro. Any other facets defined on the complex type are ignored.
  • If the schema defines a single root element, the tool will emit a single Avro record type. If the schema defines multiple root elements, the tool will emit a union of record types, each corresponding to a root element.
  • All fields in the resulting Avro Schema are annotated with an xmlkind extension attribute that indicates whether the field was an element or an attribute in the XML schema.

Convert Avro schema to XML schema

avrotize a2x --avsc <path_to_avro_schema_file> --xsd <path_to_xsd_schema_file>

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --xsd: The path to the XML schema file to write the conversion result to.

Conversion notes:

  • Avro record types are mapped to XML Schema complex types with elements.
  • Avro enum types are mapped to XML Schema simple types with restrictions.
  • Avro logical types are mapped to XML Schema simple types with restrictions where required.
  • Avro unions are mapped to standalone XSD simple type definitions with a union restriction if all union types are primitives.
  • Avro unions with complex types are resolved into distinct types for each option that are then joined with a choice.

Convert ASN.1 schema to Avro schema

avrotize asn2a --asn <path_to_asn1_schema_file>[,<path_to_asn1_schema_file>,...]  --avsc <path_to_avro_schema_file>

Parameters:

  • --asn: The path to the ASN.1 schema file to be converted. The tool supports multiple files in a comma-separated list.
  • --avsc: The path to the Avro schema file to write the conversion result to.

Conversion notes:

  • All ASN.1 types are mapped to Avro record types, enums, and unions. Avro does not support the same level of nesting of types as ASN.1, the tool will map the types to the best fit.
  • The tool will map the following ASN.1 types to Avro types:
    • SEQUENCE and SET are mapped to Avro record types.
    • CHOICE is mapped to an Avro record types with all fields being optional. While the CHOICE type technically corresponds to an Avro union, the ASN.1 type has different named fields for each option, which is not a feature of Avro unions.
    • OBJECT IDENTIFIER is mapped to an Avro string type.
    • ENUMERATED is mapped to an Avro enum type.
    • SEQUENCE OF and SET OF are mapped to Avro array type.
    • BIT STRING is mapped to Avro bytes type.
    • OCTET STRING is mapped to Avro bytes type.
    • INTEGER is mapped to Avro long type.
    • REAL is mapped to Avro double type.
    • BOOLEAN is mapped to Avro boolean type.
    • NULL is mapped to Avro null type.
    • UTF8String, PrintableString, IA5String, BMPString, NumericString, TeletexString, VideotexString, GraphicString, VisibleString, GeneralString, UniversalString, CharacterString, T61String are all mapped to Avro string type.
    • All other ASN.1 types are mapped to Avro string type.
  • The ability to parse ASN.1 schema files is limited and the tool may not be able to parse all ASN.1 files. The tool is based on the Python asn1tools package and is limited to that package's capabilities.

Convert Kusto table definition to Avro schema

avrotize k2a --kusto-uri <kusto_cluster_uri> --kusto-database <kusto_database> --avsc <path_to_avro_schema_file> --emit-cloudevents-xregistry

Parameters:

  • --kusto-uri: The URI of the Kusto cluster to connect to.
  • --kusto-database: The name of the Kusto database to read the table definitions from.
  • --avsc: The path to the Avro schema file to write the conversion result to.
  • --emit-cloudevents-xregistry: (optional) See discussion below.

Conversion notes:

  • The tool directly connects to the Kusto cluster and reads the table definitions from the specified database. The tool will convert all tables in the database to Avro record types, returned in a top-level type union.
  • Connecting to the Kusto cluster leans on the same authentication mechanisms as the Azure CLI. The tool will use the same authentication context as the Azure CLI if it is installed and authenticated.
  • The tool will map the Kusto column types to Avro types as follows:
    • bool is mapped to Avro boolean type.
    • datetime is mapped to Avro long type with logical type timestamp-millis.
    • decimal is mapped to a logical Avro type with the logicalType set to decimal and the precision and scale set to the values of the decimal type in Kusto.
    • guid is mapped to Avro string type.
    • int is mapped to Avro int type.
    • long is mapped to Avro long type.
    • real is mapped to Avro double type.
    • string is mapped to Avro string type.
    • timespan is mapped to a logical Avro type with the logicalType set to duration.
  • For dynamic columns, the tool will sample the data in the table to determine the structure of the dynamic column. The tool will map the dynamic column to an Avro record type with fields that correspond to the fields found in the dynamic column. If the dynamic column contains nested dynamic columns, the tool will recursively map those to Avro record types. If records with conflicting structures are found in the dynamic column, the tool will emit a union of record types for the dynamic column.
  • If the --emit-cloudevents-xregistry option is set, the tool will emit an xRegistry registry manifest file with a CloudEvent message definition for each table in the Kusto database and a separate Avro Schema for each table in the embedded schema registry. If one or more tables are found to contain CloudEvent data (as indicated by the presence of the CloudEvents attribute columns), the tool will inspect the content of the type (or __type or __type) columns to determine which CloudEvent types have been stored in the table and will emit a CloudEvent definition and schema for each unique type.

Convert Avro schema to Kusto table declaration

avrotize a2k --avsc <path_to_avro_schema_file> --kusto <path_to_kusto_kql_file> [--record-type <record_type>] [--emit-cloudevents-columns] [--emit-cloudevents-dispatch]

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --kusto: The path to the Kusto KQL file to write the conversion result to.
  • --record-type: (optional) The name of the Avro record type to convert to a Kusto table.
  • --emit-cloudevents-columns: (optional) If set, the tool will add CloudEvents attribute columns to the table: ___id, ___source, ___subject, ___type, and ___time.
  • --emit-cloudevents-dispatch: (optional) If set, the tool will add a table named _cloudevents_dispatch to the script or database, which serves as an ingestion and dispatch table for CloudEvents. The table has columns for the core CloudEvents attributes and a data column that holds the CloudEvents data. For each table in the Avro schema, the tool will create an update policy that maps events whose type attribute matches the Avro type name to the respective table.

Conversion notes:

  • Only the Avro record type can be mapped to a Kusto table. If the Avro schema contains other types (like enum or array), the tool will ignore them.
  • Only the first record type in the Avro schema is converted to a Kusto table. If the Avro schema contains other record types, they will be ignored. The --record-type option can be used to specify which record type to convert.
  • The fields of the record are mapped to columns in the Kusto table. Fields that are records or arrays or maps are mapped to columns of type dynamic in the Kusto table.

Convert Avro schema to T-SQL table definition

avrotize a2tsql --avsc <path_to_avro_schema_file> --tsql <path_to_sql_file> [--record-type <record_type>] [--emit-cloudevents-columns]

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --tsql: The path to the T-SQL file to write the conversion result to.
  • --record-type: (optional) The name of the Avro record type to convert to a T-SQL table.
  • --emit-cloudevents-columns: (optional) If set, the tool will add CloudEvents attribute columns to the table: __id, __source, __subject, __type, and __time.

Conversion notes:

  • Only the Avro record type can be mapped to a T-SQL table. If the Avro schema contains other types (like enum or array), the tool will ignore them.
  • Only the first record type in the Avro schema is converted to a T-SQL table. If the Avro schema contains other record types, they will be ignored. The --record-type option can be used to specify which record type to convert.
  • The fields of the record are mapped to columns in the T-SQL table. Fields of type record or array or map are mapped to columns of type varchar(max) in the T-SQL table and it's assumed for them to hold JSON data.
  • The emitted script sets extended properties to the columns with the Avro schema definition of the field in a JSON format. This allows for easy introspection of the serialized Avro schema in the field definition.

Convert Avro schema to empty Parquet file

avrotize a2pq --avsc <path_to_avro_schema_file> --parquet <path_to_parquet_schema_file> [--record-type <record-type-from-avro>] [--emit-cloudevents-columns]

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --parquet: The path to the Parquet schema file to write the conversion result to.
  • --record-type: (optional) The name of the Avro record type to convert to a Parquet schema.
  • --emit-cloudevents-columns: (optional) If set, the tool will add CloudEvents attribute columns to the Parquet schema: __id, __source, __subject, __type, and __time.

Conversion notes:

  • The emitted Parquet file contains only the schema, no data rows.
  • The tool only supports writing Parquet files for Avro schema that describe a single record type. If the Avro schema contains a top-level union, the --record-type option must be used to specify which record type to emit.
  • The fields of the record are mapped to columns in the Parquet file. Array and record fields are mapped to Parquet nested types. Avro type unions are mapped to structures, not to Parquet unions since those are not supported by the PyArrow library used here.

Convert Parquet schema to Avro schema

avrotize pq2a --parquet <path_to_parquet_schema_file> --avsc <path_to_avro_schema_file> --namespace <avro_schema_namespace>

Parameters:

  • --parquet: The path to the Parquet file whose schema is to be converted.
  • --avsc: The path to the Avro schema file to write the conversion result to.
  • --namespace: The namespace to use in the Avro schema.

Conversion notes:

  • The tool reads the schema from the Parquet file and converts it to an Avro schema. The Avro schema is written to the specified file.

Generate C# code from Avro schema

avrotize a2csharp --avsc <path_to_avro_schema_file> --csharp <path_to_csharp_directory> [--avro-annotation] [--system-text-json-annotation] [--newtonsoft-json-annotation] [--pascal-properties]

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --csharp: The path to the C# directory to write the conversion result to.
  • --avro-annotation: (optional) If set, the tool will add Avro annotations to the C# classes.
  • --system-text-json-annotation: (optional) If set, the tool will add System.Text.Json annotations to the C# classes.
  • --newtonsoft-json-annotation: (optional) If set, the tool will add Newtonsoft.Json annotations to the C# classes.
  • --pascal-properties: (optional) If set, the tool will use PascalCase properties in the C# classes.
  • --namespace: (optional) The namespace to use in the generated C# classes.

Conversion notes:

  • The tool generates C# classes that represent the Avro schema as data classes.
  • Using the --system-text-json-annotation or --newtonsoft-json-annotation option will add annotations for the respective JSON serialization library to the generated C# classes. Because the JSON Schema to Avro conversion generally preserves the JSON Schema structure in the Avro schema, the generated C# classes can be used to serialize and deserialize data that is valid per the input JSON schema.
  • Only the --system-text-json-annotation option generates classes that support type unions.
  • The classes are generated into a directory structure that reflects the Avro namespace structure. The tool drops a minimal, default .csproj project file into the given directory if none exists.

Read more about the C# code generation in the C# code generation documentation.

Generate Java code from Avro schema

avrotize a2java --avsc <path_to_avro_schema_file> --java <path_to_java_directory> [--package <java_package_name>] [--avro-annotation] [--jackson-annotation] [--pascal-properties]

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --java: The path to the Java directory to write the conversion result to.
  • --package: (optional) The Java package name to use in the generated Java classes.
  • --avro-annotation: (optional) If set, the tool will add Avro annotations to the Java classes.
  • --jackson-annotation: (optional) If set, the tool will add Jackson annotations to the Java classes.
  • --pascal-properties: (optional) If set, the tool will use PascalCase properties in the Java classes.

Conversion notes:

  • The tool generates Java classes that represent the Avro schema as data classes.
  • Using the --jackson-annotation option will add annotations for the Jackson JSON serialization library to the generated Java classes. Because the JSON Schema to Avro conversion generally preserves the JSON Schema structure in the Avro schema, the generated Java classes can be used to serialize and deserialize data that is valid per the input JSON schema.
  • The directory /src/main/java is created in the specified directory and the generated Java classes are written to this directory. The tool drops a minimal, default pom.xml Maven project file into the given directory if none exists.

Read more about the Java code generation in the Java code generation documentation.

Generate Python code from Avro schema

This command generates Python dataclasses from an Avro schema.

avrotize a2py --avsc <path_to_avro_schema_file> --python <path_to_python_directory> [--package <python_package_name>]

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --python: The path to the Python directory to write the conversion result to.
  • --package: (optional) The Python package name to use in the generated Python classes.
  • --avro-annotation: (optional) If set, the tool will add Avro annotations to the Python classes.
  • --dataclasses-json-annotation: (optional) If set, the tool will add dataclasses-json annotations to the Python classes

Conversion notes:

  • The tool generates Python dataclasses (Python 3.7 or later)
  • The classes are generated into a directory structure that reflects the Avro namespace structure. The tool drops a minimal, default __init__.py file into any created package directories if none exists.

Generate TypeScript code from Avro schema

avrotize a2ts --avsc <path_to_avro_schema_file> --ts <path_to_typescript_directory> [--package <typescript_namespace>] [--avro-annotation] [--typedjson-annotation]

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --ts: The path to the TypeScript directory to write the conversion result to.
  • --package: (optional) The TypeScript namespace to use in the generated TypeScript classes.
  • --avro-annotation: (optional) If set, the tool will add Avro annotations to the TypeScript classes.
  • --typedjson-annotation: (optional) If set, the tool will add TypedJSON annotations to the TypeScript classes.

Conversion notes:

  • The tool generates TypeScript interfaces that represent the Avro schema as data classes.
  • Using the --typedjson-annotation option will add annotations for the TypedJSON JSON serialization library to the generated TypeScript classes. Because the JSON Schema to Avro conversion generally preserves the JSON Schema structure in the Avro schema, the generated TypeScript classes can be used to serialize and deserialize data that is valid per the input JSON schema.
  • The classes are generated into a directory structure that reflects the Avro namespace

Generate JavaScript code from Avro schema

avrotize a2js --avsc <path_to_avro_schema_file> --js <path_to_javascript_directory> [--package <javascript_namespace>] [--avro-annotation]

Parameters:

  • --avsc: The path to the Avro schema file to be converted.
  • --js: The path to the JavaScript directory to write the conversion result to.
  • --package: (optional) The JavaScript namespace to use in the generated JavaScript classes.
  • --avro-annotation: (optional) If set, the tool will add Avro annotations to the JavaScript classes.

Conversion notes:

  • The tool generates JavaScript classes that represent the Avro schema as data classes.
  • The classes are generated into a directory structure that reflects the Avro namespace

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

Avrotize is released under the Apache License. See the LICENSE file for more details.

About

Avrotize is a command-line tool for converting data structure definitions between different schema formats, using Apache Avro Schema as the integration schema model.

asn1avroavro-schemaavro-schemasjson-schemaprotobufprotocol-buffersxsdxsd-schemacsharpjavajavascripttypescript

License:Apache License 2.0

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