langchain-opensolr

LangChain integration for Opensolr — managed Apache Solr with server-side embeddings and native hybrid (BM25 + kNN) search.

See it live (real news index, hybrid + AI answer): https://search.opensolr.com/news__dense?q=how+am+I+supposed+to+save+money%3F

Product page: opensolr.com/langchain · Platform: opensolr.com (managed Solr hosting since 2011 — free forever, no card)

No local embedding model. No third-party embedding API key. One set of credentials, and the vectors are computed on Opensolr's GPU infrastructure (multilingual E5-large-instruct, 1024 dimensions, cosine).

pip install langchain-opensolr

The whole tutorial

from langchain_opensolr import OpensolrVectorStore

vs = OpensolrVectorStore(
    index="mysite__dense",          # vector-enabled Opensolr index
    email="you@example.com",
    api_key="YOUR_OPENSOLR_API_KEY",
    create_if_missing=True,          # provisions the index on first use
)

vs.add_texts(
    ["Hybrid search fuses BM25 with vector similarity",
     "Cats sleep sixteen hours a day"],
    metadatas=[{"category": "search"}, {"category": "animals"}],
)

docs = vs.similarity_search("how do lexical and semantic search combine?", k=1)
print(docs[0].page_content)

That's it — no embedding model was configured, because embedding happens on the server at both index and query time.

Try it without an account

There is a public demo account. Point the package at it and everything in this README works immediately, with no signup:

export OPENSOLR_EMAIL=mcp@opensolr.com
export OPENSOLR_API_KEY=420b8b23e7b12dc8ab838932145a5065

mcp_demo_d1__dense is already loaded with 300 news articles, so search, filtering and grounded answers work the moment you connect. You also get the write path: create your own index on the account, ingest into it and query it. Deletion is not available on this shared key: no index here can be deleted or reconfigured by hand. Whatever you create is removed automatically after 3 days.

Know what you are working with:

• Anything you create there is deleted after 3 days. Automatically, without warning or export. That includes indexes you created and every document in them.
• The account is shared with everyone reading this. Your index is visible to them and they can add documents to it, as you can to theirs. Nobody can delete or reconfigure an index here (that is switched off for this key), but never put anything real, private or client-owned in it.
• The limits are per index, and deliberately small. 200 MB of bandwidth and 50 MB of disk per index. Bandwidth is the one you will hit first: it covers a demo, a tutorial and a proof of concept, and it will not carry an application.

When you want an index that is private, yours and still there next week, get your own key — free forever, no card — and change the two variables above. Nothing else in your code changes.

Hybrid search

Pure vector search fails on exact identifiers; pure BM25 fails on meaning. Opensolr's {!hybrid} query parser fuses both scores per document:

docs = vs.similarity_search(
    "affordable restaurants",
    k=5,
    hybrid=True,
    mode="union",     # union | keywords_required | meaning_required | intersection
    alpha=0.5,        # 0 = all semantic … 1 = all lexical
)

Search operators

The query string understands the operators people already expect from a search box. They work in every mode — keyword, hybrid and pure vector.

They compose: +laptop +"13 inch" -refurbished returns only 13-inch laptops and never a refurbished one.

A prefixed term (+ or -, word or phrase) becomes a filter, applied to the whole result set. That matters as soon as a vector is involved: the semantic side of a hybrid search has no concept of negation, so left as query text -refurbished would actually pull refurbished listings towards the top rather than removing them. As a filter it binds every document, whichever side of the search found it, and the exclusion is absolute.

An unprefixed phrase ("machine learning" with no + in front) is a keyword-side relevance signal rather than a filter — use +"machine learning" when you need it enforced.

+ and - only count at the start of a word, so e-mail, covid-19 and 1+1 are searched for literally.

Metadata filters

vs.similarity_search("search engines", k=5, filter={"category": "search"})
vs.similarity_search("anything", k=5, filter='meta_rank:[2 TO *]')   # raw Solr fq

Metadata round-trips losslessly (stored as JSON alongside filterable meta_* fields).

As a retriever, in any chain

retriever = vs.as_retriever(search_kwargs={"k": 5, "hybrid": True})

Standalone embeddings

Use Opensolr's embedding endpoint with any other LangChain component:

from langchain_opensolr import OpensolrEmbeddings

emb = OpensolrEmbeddings(email="you@example.com", api_key="...", index="mysite__dense")
emb.embed_query("budget-friendly dining")   # -> 1024 floats

Notes

• Vector-enabled indexes run on Opensolr's Solr 9.x environments — currently us (Chicago), de (Germany), fi (Finland). Pass location= to choose. The list is fetched live from the platform, so new regions work without a package upgrade — and additional dedicated regions can be deployed on request (paid add-on): support@opensolr.com.
• A free Opensolr account (free forever, no card) includes an AI quota that comfortably covers this README end to end: opensolr.com.
• Full platform docs: AI & Vector Search.

Development

pip install -e . pytest
pytest tests/unit_tests
OPENSOLR_EMAIL=... OPENSOLR_API_KEY=... OPENSOLR_INDEX=... pytest tests/integration_tests

How writing works (Data Ingestion API)

Writes go through Opensolr's Data Ingestion API — the same pipeline the Drupal and WordPress connectors use. It is asynchronous: documents are queued, then embeddings, sentiment, language and all crawler-identical derived fields are computed server-side, and documents become searchable within about a minute. Progress is visible in Control Panel → Data Ingestion — a per-job status board (queued / processing / completed / failed, with processed / success / failed document counts per job) — and via the ingest_status API. Each document's identity is its uri (the Solr id is md5(uri)): pass a real URL in metadata ({"uri": "https://..."}), or a deterministic one is synthesized from your id. Re-submitting the same uri updates the document. Pass {"rtf": True, "uri": "https://.../file.pdf"} and the server extracts the text from PDF/DOCX/XLSX for you.

Lexical-only mode

Don't need vectors? Pure keyword search skips the embedding call entirely — zero AI quota, and it works on any Opensolr index, including non-vector ones and older Solr versions.

Search by image

Search your index with a photo instead of a text query. Opensolr reads the picture three ways — visual labels (what it depicts), OCR text (words printed on it), and any barcode / QR code — and turns that into an ordinary search. Nothing new is stored in Solr; the picture simply becomes words.

# What the picture reads as (labels, OCR text, barcodes) — no search yet:
read = vs.image_to_words("photo.jpg")     # path, bytes, or base64
# {'text': 'red running shoe', 'mode': 'clip',
#  'labels': ['running shoe', 'sneaker'], 'codes': ['0123456789012']}

# Search the index with the picture:
docs = vs.search_by_image("photo.jpg", k=4)          # engine picks the best reading
docs = vs.search_by_image("photo.jpg", using="meaning")  # visual labels
docs = vs.search_by_image("photo.jpg", using="text")     # only OCR text
docs = vs.search_by_image("photo.jpg", using="code")     # exact barcode / QR match
docs = vs.search_by_image("photo.jpg", using="all")      # labels + OCR + codes

search_by_image accepts the same tuning as similarity_search — hybrid, mode, alpha, fresh_bias, filter — so an image query runs through the exact hybrid pipeline a text query does.

Local files: PDFs page by page, scans through OCR

Read a file or a whole folder into LangChain Documents with OpensolrLoader — one Document per PDF page (metadata["page"], from 1), one per any other file:

from langchain_opensolr import OpensolrLoader

loader = OpensolrLoader("./contracts", index="mysite__dense",
                        email="you@example.com", api_key="YOUR_OPENSOLR_API_KEY",
                        pattern="*.pdf")
docs = loader.load()          # or loader.lazy_load()
# metadata: source, page, is_ocr, language, content_type

Or index them straight into the store — no splitting, no loader, PDFs page by page:

result = vs.add_files("./contracts", pattern="*.pdf", metadata={"team": "legal"}, wait=True)
# {"documents": [{path, source, uri, id}], "pending": [], "failed": [], "jobs": [...]}

• Each file is read on Opensolr's servers: its text, the text in its pictures (OCR, more than 100 languages), a short description of the pictures without text. Word, RTF, OpenDocument, text, HTML and picture files (scans) are one document each; a PDF is one document per page.
• The bytes travel once: a file the account already sent (same content) is not uploaded again. Pictures read by OCR count 0.5 of an AI request each; a file read before is free.
• Files still being read when timeout runs out are listed in loader.pending (or result["pending"]): run again to get them, nothing is sent twice. Files that could not be read are in loader.failed / result["failed"].
• An indexed file's uri is https://ingest.opensolr.com/<index>/<source>, where source is its path from the folder you sent (metadata["source"] on every hit); sending it again replaces it. Its date is the file's modification time.

PDF pages in search results

On an index where PDFs are stored page by page (files indexed as above, PDFs sent to Data Ingestion with rtf, PDFs found by the Web Crawler), a search returns each PDF once, as its best page. Its metadata carries page (the page number), page_url (opens the PDF at that page, ...pdf#page=14), document_id, more_pages (its other matching pages, each with page and page_url) and matching_pages; every hit carries its uri. group_pages=False returns the pages as separate results.

Searching a period

date_from and date_to (YYYY-MM-DD, both included, either one can be left out) keep only the documents dated in that period (creation_date):

docs = vs.similarity_search("rate decision", k=5, hybrid=True,
                            date_from="2026-01-01", date_to="2026-03-31")

They combine with every other option — filters, fresh_bias, hybrid or lexical.

Your index schema

Documents follow the Opensolr document model (title, description, text, meta_* custom fields). The whole schema, every field and every type suffix, is explained in the Index Schema Reference. To see your own copy: Control Panel → click your index → Configuration → Edit File → schema.xml. Prefer zero-effort data entry? Configure the Web Crawler in the Control Panel (Index Tools → WebCrawler): add your site URL, validate it, and Opensolr indexes the whole site for you.

Grounded RAG answers

One call: hybrid retrieval picks the top hits, whose content becomes the LLM context, and Opensolr's server-side LLM answers — the same pipeline that powers the AI answers on our hosted search pages. No LLM key, no chain to assemble:

answer = vs.ai_answer(
    "what does the refund policy say?",
    rag_docs=3,        # how many hybrid hits feed the LLM (default 3)
    rag_words=1500,    # words of text taken from each hit (default 1500)
    # instruction="Answer in German, cite the exact titles you used",  # optional
)

Search tuning

Retrieval (search and RAG grounding) runs through the platform's tuned pipeline: global defaults → your index's saved Search Tuning (Control Panel → Index Settings → Search Tuning: semantic↔lexical balance, field weights, minimum match, search mode, vector candidate pool, content quality boost) → optional per-call overrides via tuning:

tuning={"search_mode": "keywords_required", "fw_title": 0.2,
        "mm": "strict", "vector_topk": 500, "quality_boost": 0.3}

Defaults match the platform's PHP configuration exactly — customize in the Control Panel once, or per call from code.

Fresh Results Bias

Rank newer documents higher without hiding anything older. Every score is multiplied by a recency curve on creation_date — full weight for a document published today, about half after a year:

store.similarity_search_with_score("solar inverter warranty", fresh_bias=True)
client.hybrid_search(index, query, fresh_bias=True)
client.ai_answer(index, question, tuning={"fresh_bias": 1})

It re-orders and never filters: the hit count is identical either way, nothing old becomes unreachable, and a document with no creation_date simply keeps its place instead of being pushed to the bottom. It applies to all three retrieval shapes — vector-only, keyword-only and the fused hybrid ranking — because the boost wraps the final score rather than one half of it. Off by default.

This is the same control visitors get as the Fresh toggle beside the sort options on the hosted Opensolr search page, so a query behaves identically here and there.

fresh_bias and freshness_boost are two different knobs and the names invite confusion. freshness_boost is a hard window in days — anything older is filtered out and the hit count drops. fresh_bias filters nothing.

How it's tested

Every release is validated against live Opensolr infrastructure — no mocks:

• Unit tests (offline): location aliases, filter→fq mapping, query building, escaping.
• End-to-end suite: the full write path through the async Data Ingestion queue (queued → server-side enrichment → searchable), semantic / hybrid / lexical retrieval, metadata round-trip, filters, id round-trip (your ids and the Solr md5(uri) ids), deletes by id and by query.
• Real-corpus validation: searches run against a 340-document replica of opensolr.com's own production search index. Verified: pure-semantic hits with zero keyword overlap ("how do I get my data back after a disaster" → backup & restore docs), cross-lingual queries (Romanian query → English content), exact-term surfacing in hybrid mode, all four hybrid modes, and the full alpha range 0 → 1.
• PDF ingestion: a real PDF ingested via rtf:true — server-side text extraction (13k+ chars), automatic content-type detection, then retrieved with a purely semantic query against its contents.
• Grounded RAG answers: ai_answer verified end-to-end — a question answerable only from the ingested PDF returns the correct answer, sourced from the PDF's extracted text via hybrid retrieval.

pytest tests/unit_tests
OPENSOLR_EMAIL=... OPENSOLR_API_KEY=... OPENSOLR_INDEX=... pytest tests/integration_tests

MIT license.