mongoeco

mongoeco is an async-first local MongoDB mock/runtime for tests, local development and embedded workflows, with a MongoDB-like surface and pluggable storage engines.

It is built for local development, test environments, embedded persistence and compatibility work where a PyMongo-shaped API is useful without requiring a real MongoDB server for every workflow. It uses CXP to expose its database/mongodb capabilities in a structured way for tooling and interoperability.

Current Scope

What is already in place:

• async and sync client APIs
• memory and SQLite engines
• transactional local sessions and local admin/runtime introspection
• aggregation runtime with pushdown and spill guardrails
• a structured CXP capability export for the local database/mongodb surface
• compatibility modeling across MongoDB dialects and PyMongo profiles
• local wire/driver runtime
• local geospatial, classic $text, $search and ANN-backed $vectorSearch

What this is not:

• a drop-in replacement for a production MongoDB cluster
• a full Atlas Search implementation
• a geodesic geospatial engine
• a full-text/vector engine with server-grade scaling guarantees

When To Use mongoeco

mongoeco fits well when you want:

• a local database/mongodb runtime for development or CI;
• a local PyMongo-like runtime without a server process;
• more semantic fidelity than a lightweight mock;
• embedded persistence with either memory or SQLite;
• local $text, $search and $vectorSearch without standing up a server;
• explicit compatibility and explain() diagnostics instead of opaque best effort behavior.

Reference:

• docs/use-cases.md
• docs/use-cases/embedded-app.md
• docs/use-cases/test-runtime.md
• docs/use-cases/local-search-and-retrieval.md
• docs/comparisons.md

Installation

Editable local install:

python -m pip install -e .

Development install:

python -m pip install -e .[dev]

MongoEco is a PEP 561 typed package. Wheels and source distributions include py.typed; the supported typing boundary covers the documented client, engine SPI v2, Search and conformance surfaces. CI checks those contracts with strict positive and negative consumer fixtures against the installed wheel.

The 4.8.0 source requires cxp[exchange]>=5.0.0,<6 and exposes its database/mongodb contract through owner-authored exchange documents. Its org.mongoeco:mongodb@1.2.0 catalog uses CXP catalog spec_version 2; snapshots and requirements pin that exact catalog while retaining their v1 document formats. Reference:

• docs/cxp-exchange.md

The public compatibility export and the top-level cxp blocks surfaced by find(...).explain() / aggregate(...).explain() are now projected from that canonical CXP capability model.

The public CXP story now includes canonical first-level operation bindings as well:

• read -> find, find_one, count_documents, estimated_document_count, distinct
• write -> insert_one, insert_many, update_one, update_many, replace_one, delete_one, delete_many, bulk_write
• aggregation -> aggregate
• change_streams -> watch
• transactions -> start_session, with_transaction

For search and vector_search, mongoeco still binds the public operation aggregate and uses metadata to describe the supported stage-level subset. That metadata also carries operation-level hints such as result shape, scope, session support and core accepted inputs for read, write and aggregation.

For reusable profile gates, the practical split is now:

• mongodb-text-search when you need textual $search without requiring vector_search;
• mongodb-search when you need both textual and vector search;
• mongodb-platform when you need the broader platform surface, including canonical metadata for collation, persistence and topology discovery.

The exchange documents publish these named profiles with exact catalog pins. The cxp block in explain() carries their evaluated verdicts for the declared library snapshot; it does not infer a minimal profile from a query path. Consumers can load each profile from mongoeco.cxp.exchange and evaluate it with a context that explicitly states accepted provenance. The compat report embeds the same documents through export_exchange_catalog(). Operational telemetry shape requirements live in Mongoeco's driver resources and are validated separately from component compatibility.

The root mongoeco package is intentionally narrower than the full runtime internals. It centers on:

• clients and session entry points
• common BSON-facing types and operation models
• URI/configuration helpers needed by the main runtime surface

Compatibility tooling and the canonical MongoDB CXP contract surface live in their own packages:

• mongoeco.compat
• mongoeco.cxp.exchange
• mongoeco.engines for the public storage-engine SPI v2
• mongoeco.conformance for versioned engine contract validation

Lower-level driver/runtime details remain available from subpackages such as mongoeco.driver.

mongoeco.compat follows the same idea: the top-level package keeps the catalog exports, profile resolution helpers and option-support surface, while more tactical constants and raw catalog data stay in explicit submodules. It also exposes deprecation_entries() and public_api_manifest() so release tooling can inspect planned removals and the semantic 4.x surface without scraping documentation. The catalog lifecycle is documented in docs/deprecations.md.

Import guidance by layer:

• use mongoeco for clients, sessions, BSON-facing types and URI/config helpers
• use mongoeco.compat for dialect/profile resolution and compat/tooling exports
• use mongoeco.cxp.exchange for pinned MongoDB compatibility documents
• use mongoeco.engines and mongoeco.conformance for third-party storage engines and their public contract tests
• use mongoeco.driver and mongoeco.wire only when you intentionally need lower-level runtime surfaces

Custom storage engines should implement the versioned SPI v2 contract. The public capability, outcome, operation-context and snapshot types are exported from mongoeco.engines; see the SPI v2 contract and the MongoEco 4.7 migration guide. Starting with 4.7, SPI v2 is the only stable engine SPI and engine capabilities must be declared explicitly.

Public Surface Stability (4.8.0 source candidate)

The 4.8.0 source candidate prepares an exchange-only breaking release. It is not published. Its import roots are explicit:

• stable import roots are mongoeco, mongoeco.compat, mongoeco.cxp.exchange, mongoeco.engines and mongoeco.conformance
• each root surface is curated through its __all__
• lower-level runtime symbols stay in explicit subpackages

The root package no longer exposes transport aliases. Import transport classes from mongoeco.driver directly.

mongoeco does not ship a live CXP provider wrapper for its clients. Instead, it exposes the canonical catalog and projects the active capability path through compat and explain(). External systems can wrap mongoeco if they want to negotiate profiles or instantiate resources through CXP.

mongoeco.cxp.exchange is the canonical compatibility source. mongoeco.compat exports those exact documents in its reporting view. See the CXP removal migration guide for import and reporting changes.

The direct path for CXP-facing tooling is:

from mongoeco import MongoClient
from mongoeco.compat import export_exchange_catalog
from mongoeco.engines.memory import MemoryEngine


print(export_exchange_catalog()["catalog_sha256"])

with MongoClient(MemoryEngine()) as client:
    collection = client.get_database("demo").get_collection("items")
    collection.insert_one({"_id": 1, "score": 8})
    explain = collection.aggregate([{"$match": {"score": {"$gte": 8}}}]).explain()
    print(explain["cxp"])

The base package now includes pyuca as a runtime dependency so Unicode collations keep a deterministic UCA-backed behavior even when PyICU is not installed.

Advanced ICU collation backend (optional):

python -m pip install PyICU

Collation backend policy:

• PyICU stays optional by contract: it is never required for the supported baseline subset
• PyICU if available: preferred backend, including advanced collation knobs such as backwards, alternate, maxVariable and normalization
• pyuca fallback: Unicode collation for the supported basic subset (locale=en, strength, caseLevel, numericOrdering)
• if advanced knobs are requested without PyICU, mongoeco raises an error instead of silently ignoring them

Optional fast JSON backend:

python -m pip install -e .[json-fast]

mongoeco uses the standard library json module by default, even if orjson is installed. You can choose the backend at process start with MONGOECO_JSON_BACKEND:

• stdlib: always use the standard library JSON backend
• orjson: require orjson and use it
• auto: use orjson when available, otherwise fall back to stdlib

Example:

MONGOECO_JSON_BACKEND=orjson python your_app.py

Runtime behavior highlights:

• the simple collation keeps using the BSON/Python baseline comparator and rejects Unicode tailoring knobs such as caseLevel or numericOrdering
• the currently supported locale surface is simple and en
• the currently supported strengths are 1, 2 and 3
• numericOrdering and caseLevel are supported for locale=en
• PyICU and pyuca are intentionally close, but may still differ on advanced tailoring details outside the currently supported locale surface
• local change streams retain a bounded in-memory history; the retention size can be tuned with change_stream_history_size on async/sync clients and on direct async database/collection constructors
• local change streams can also persist that retained history to a journal file with change_stream_journal_path, allowing resume_after / start_after to survive client recreation inside the same local environment
• the journal can also be hardened with change_stream_journal_fsync=True and bounded by size with change_stream_journal_max_bytes
• when journaling is enabled, mongoeco keeps an incremental event log and compacts it back into a retained snapshot as the local history rolls forward; each log entry carries an integrity checksum and truncated tail writes are ignored on reload
• clients, databases and direct collections expose change_stream_state() so local retained history, journal files and compaction progress can be inspected at runtime
• clients, databases and direct collections also expose change_stream_backend_info(), which makes the contract explicit: change streams are local, optionally persistent via journal, resumable inside that local environment, and not distributed across nodes
• the local driver now starts non-direct single-seed topologies as provisional UNKNOWN and relies on hello discovery to converge towards standalone, replicaSet or sharded topology shapes
• retryable reads and writes now apply to real wire connection failures too: connect/read/write socket errors are normalized to ConnectionFailure
• replica-set discovery also tracks per-server health states (healthy, recovering, degraded, unreachable) and uses them to prefer healthier candidates when ordering eligible servers
• clients expose sdam_capabilities() so the supported SDAM subset is inspectable at runtime instead of being implicit in the implementation
• mongoeco.collation_backend_info() reports the active Unicode backend, while mongoeco.collation_capabilities_info() reports the supported locale surface and which advanced knobs require PyICU

Quick Start

Async with the in-memory engine:

import asyncio

from mongoeco import AsyncMongoClient
from mongoeco.engines.memory import MemoryEngine


async def main() -> None:
    async with AsyncMongoClient(MemoryEngine()) as client:
        collection = client.demo.users
        await collection.insert_one({"_id": "1", "name": "Ada"})
        document = await collection.find_one({"name": "Ada"})
        print(document)


asyncio.run(main())

Sync with SQLite:

from mongoeco import MongoClient
from mongoeco.engines.sqlite import SQLiteEngine


with MongoClient(SQLiteEngine("mongoeco.db")) as client:
    collection = client.demo.users
    collection.insert_one({"_id": "1", "name": "Ada"})
    print(collection.find_one({"_id": "1"}))

Examples

Executable examples live under examples/README.md:

• memory_quickstart.py
• sqlite_embedded_app.py
• test_runtime_local.py
• search_and_vector_local.py
• vector_search_diagnostics.py
• cxp_adapter.py

The local $search subset now includes:

• text
• phrase with optional slop
• autocomplete
• wildcard
• regex
• exists
• in
• equals
• range
• near
• compound
• this local textual tier is now considered closed in its documented subset; what remains is advanced Atlas-like behavior, not the daily embedded perimeter.
• the advanced local subset now also exposes:
  • autocomplete.tokenOrder with any / sequential
  • regex.flags with i / m / s / x
  • wildcard.allowAnalyzedField
  • $search.count, $search.highlight and $search.facet as local stage options; highlight metadata is projectable through $meta: "searchHighlights", while the legacy searchHighlights field is injected only when it does not collide with user data
  • $searchMeta typed count/facet collectors and explain("queryPlanner"|"executionStats"); legacy previews remain only as deprecated 4.x aliases

Examples worth showing first:

• test_runtime_local.py demonstrates MemoryEngine and SQLiteEngine as local contract runtimes with the same $search.phrase behavior.
• search_and_vector_local.py demonstrates exact phrase versus phrase.slop, numeric near, richer local search field mappings including explicit document and embeddedDocuments paths, parent-path resolution for metadata and contributors, numeric/date near, parent-path exists over structured mappings, parent-path autocomplete / wildcard / regex over structured mappings with resolved descendant leaf paths in explain(), explicit operator querySemantics, consistent scalar pathSummary metadata for equals / range / near, scalar filters over embedded-document paths, searchHighlights in local result documents, count / facet previews in explain(), and a local compound query with visible embedded path/ranking explain metadata plus equals + in + range + near + exists + regex.
• vector_search_diagnostics.py compares MemoryEngine and SQLiteEngine for local hybrid retrieval, including scoreBreakdown, candidatePlan, hybridRetrieval, pruningSummary, prefilterSources, projected vectorSearchScore, residual filtering and exact fallback in local $vectorSearch.
• cxp_adapter.py demonstrates the canonical CXP database/mongodb catalog and the cxp projection exposed by aggregate(...).explain().

Compatibility

mongoeco now exposes three public contract layers:

• the canonical CXP capability model for database/mongodb
• MongoDB server semantics through mongodb_dialect
• PyMongo surface compatibility through pymongo_profile

Planning mode is a third, separate concern:

• STRICT fails fast when a query, update or aggregation shape is not executable under the current runtime
• RELAXED preserves the request metadata and reports planning_issues instead of compiling an executable plan for unsupported shapes

See:

• COMPATIBILITY.md
• DIALECTS.md
• docs/architecture/index.md
• docs/comparisons.md

Testing

The repository uses pytest as the primary test runner:

python -m pip install -e .[dev,wire]
python -m pytest -q

Contract-testing rule for new features:

• every new public feature should land with async/sync parity coverage when both surfaces expose it
• engine-visible behavior should also add cross-engine parity coverage for MemoryEngine and SQLiteEngine whenever the contract is meant to be shared
• regressions caused by facade reconstruction (with_options(), database, get_collection(), rename()) should be fixed with explicit tests for the inherited runtime options involved, not only with the implementation change
• feature work that changes public errors or degraded planning behavior should pin the relevant user-facing message or error shape in tests

Architecture reference:

• docs/architecture/index.md

External storage engines can validate SPI v2 with the framework-neutral public kit documented in docs/engine-conformance.md. The optional engine-testing extra adds the pytest assertion helper without making pytest a runtime dependency. The repository also keeps an independent canary engine that imports only mongoeco.engines; scripts/smoke_external_engine.py executes it against the installed distribution.

The same runner is available as a stable CLI layer:

python -m mongoeco.conformance package.engine:factory \
  --format json \
  --output conformance.json \
  --require-success

Search planning and runtime provenance additionally use deterministic Hypothesis suites. The default ci profile is small, reproducible and runs on each PR; the scheduled Contract fuzz workflow selects the deeper profile. Planner regressions block on semantic plan and work counters, not elapsed wall time. Benchmarks remain trend evidence rather than timing gates.

Benchmarks

There is a benchmark harness under benchmarks/README.md intended for reproducible local profiling, regression tracking and community-facing performance analysis.

Quick smoke run:

python -m benchmarks.run \
  --engine all \
  --size 1000 \
  --warmup 0 \
  --repetitions 1

The harness currently covers:

• reads and point lookups;
• sort/limit and cursor materialization;
• mostly-streamable vs materializing aggregation;
• targeted local search and vectorSearch diagnostics.

Current rule of thumb from local diagnostics:

• MemoryEngine remains strongest on many Python-baseline filter paths;
• SQLiteEngine is strongest when it can push work to SQL, FTS5 or usearch;
• wildcard, exists, in, equals, range and some compound search shapes in SQLite now use a mix of materialized candidate prefilters and exact Python matching, depending on the operator/backend path;
• vectorSearch on SQLite is already materially faster than the exact baseline when the ANN backend is materialized.
• the public vector diagnostics also expose similarity, effective numCandidates, candidate evaluation counts and exact fallback reasons in benchmark metadata, so benchmark discussions can stay concrete instead of anecdotal.

For anything you plan to cite publicly, use the reproducible commands in benchmarks/README.md instead of copying ad hoc local numbers into docs.

Project Status

MongoEco 4.x is a stable package line governed by Semantic Versioning. The public API and engine SPI v2 are supported contracts. MongoEco 4.7 deliberately removes the deprecated engine SPI v1 within a minor release; this documented exception to Semantic Versioning is a product decision, not an inferred compatibility guarantee.

The unpublished 4.8.0 source makes a second explicit minor-version exception for removal of its legacy CXP surface. Its exchange replacement and public API diff are documented in the CXP migration guide.

Release-readiness checklist:

• docs/release-checklist.md
• docs/release-4.7.0.md
• docs/migrating-to-4.7.md
• docs/migrating-to-5.0.md
• docs/roadmap-5.0.md
• TODO.md
• MISSING_FEATURES.md

License

This project is licensed under the Apache License 2.0. See LICENSE.