Bug: Tables with AttributeAdapter columns raise `AssertionError: Declaration context is not set`

[zhenruiliao]

Bug Report

Description

Tables with AttributeAdapter columns raise AssertionError: Declaration context is not set on attempting to drop and when used as foreign keys. This seems to be because context is not passed down from origin table to FreeTable when it is created internally

Reproducibility

Include:

• OS (WIN | MACOS | Linux)
• Python Version 3.14
• MySQL Version Mariadb 12.0.2
• MySQL Deployment Strategy local-native
• DataJoint Version '0.14.6'
• dj-attributeadapter-test.py

Expected Behavior

Normal drop and foreign key behavior

Additional Research and Context

I have created a fork in which I simply pass context down to FreeTable, which seems to resolve the issue
Is there any reason not to pass context down?
https://github.com/zhenruiliao/datajoint-python/tree/pass-context-down-to-freetable

[dimitri-yatsenko]

Solved in #1289

[dimitri-yatsenko]

DataJoint 2.0 Solution

This issue is resolved in DataJoint 2.0 by replacing the AttributeAdapter system entirely with a new Codec system.

Root Cause

The legacy AttributeAdapter required a "declaration context" (the Python module where the table was defined) to resolve custom type adapters. When DataJoint internally created FreeTable objects for dependency tracking and foreign key resolution, it failed to pass this context, causing the AssertionError.

2.0 Architecture

DataJoint 2.0 introduces a new Codec system that eliminates context dependencies:

# Define a custom codec (auto-registers on subclass)
class GraphCodec(dj.Codec):
    name = "graph"  # Used as <graph> in definitions

    def get_dtype(self, is_external: bool) -> str:
        return "<blob>"

    def encode(self, graph, *, key=None, store_name=None):
        return {'nodes': list(graph.nodes()), 'edges': list(graph.edges())}

    def decode(self, stored, *, key=None):
        import networkx as nx
        G = nx.Graph()
        G.add_nodes_from(stored['nodes'])
        G.add_edges_from(stored['edges'])
        return G

# Use in table definitions with angle bracket syntax
class Connectivity(dj.Manual):
    definition = '''
    id : int
    ---
    graph_data : <graph>
    '''

Why This Fixes the Issue

Legacy AttributeAdapter	2.0 Codec System
Context-dependent resolution	Global codec registry
Required module inspection	Auto-registration on subclass
FreeTable context issues	No context dependency
Decorator-based registration	Automatic via __init_subclass__

The architectural flaw that caused this issue no longer exists - codecs are looked up from a global registry (_codec_registry) rather than requiring module context to be passed through the call chain.

Migration

Replace AttributeAdapter subclasses with Codec subclasses:

• Implement get_dtype(), encode(), and decode() methods
• Set the name class attribute
• Use <name> syntax in table definitions

See PR #1289 for the full implementation.

[dimitri-yatsenko]

Resolved in DataJoint 2.0

The AttributeAdapter system has been replaced by the new Codec architecture in DataJoint 2.0.

Migration path:

AttributeAdapters should be migrated to Codecs:

Before (AttributeAdapter):

class MyAdapter(dj.AttributeAdapter):
    attribute_type = 'longblob'
    def put(self, obj): ...
    def get(self, value): ...

After (Codec):

class MyCodec(dj.Codec):
    python_type = MyClass
    dj_type = '<blob>'
    def encode(self, obj): ...
    def decode(self, value): ...

Benefits of Codec system:

• Automatic registration via __init_subclass__
• No context/declaration issues
• Codec chaining support
• Built-in validation

The specific bug with declaration context is not applicable to the new Codec system.

See the migration guide for detailed migration instructions.