examples: add RAG implementation using Milvus and Gemini

examples/googleai-milvus-rag-example/README.md

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+# Google Gemini + Milvus RAG Example
+
+Welcome to the **Google Gemini + Milvus RAG Example**!  
+This Go example demonstrates how to build a simple **Retrieval-Augmented Generation (RAG)** pipeline using the [`langchaingo`](https://github.com/tmc/langchaingo) library, **Google Gemini** for embeddings and text generation, and **Milvus** as a vector database.
+
+This example shows how you can combine vector search with large language models to answer questions based on your own documents — a foundation for building intelligent knowledge assistants, search tools, and chatbots.
+
+---
+
+## 🧩 What This Example Does
+
+This example program:
+
+1. Connects to the **Google Gemini API** using your API key.
+2. Connects to a **Milvus** instance (local or cloud).
+3. Embeds and inserts a few sample documents into Milvus.
+4. Performs a **semantic similarity search** for a given query.
+5. Sends the retrieved information to Gemini for a natural-language answer.
+
+---
+
+## ⚙️ How It Works
+
+1. **Environment Setup**
+   - Loads the following environment variables:
+     - `GEMINI_API_KEY` → Required. Your Google Gemini API key.
+     - `MILVUS_URL` → Required. Address of your Milvus instance (`localhost:19530` for local Milvus, or your cloud endpoint).
+     - `MILVUS_API_KEY` → Optional. Only required for Milvus cloud instances.
+
+2. **Embedding & Storage**
+   - The program uses Gemini’s embedding model (`gemini-embedding-001`) to convert text into vectors.
+   - These vectors are stored in Milvus under the collection name `"docs"`.
+
+3. **Retrieval**
+   - A similarity search is performed for the query `"What is machine learning?"`.
+   - Milvus returns the top documents with the highest similarity scores.
+
+4. **Answer Generation**
+   - The relevant text is provided to Gemini (`gemini-2.0-flash`) to generate a clear, concise English answer.
+
+---
+
+## 🪄 Example Documents
+
+The following example notes are stored in Milvus:
+
+- “The capital of France is Paris. It is known for its culture, art, and cuisine.”  
+- “Machine learning is a branch of artificial intelligence that enables systems to learn from data and improve over time without being explicitly programmed.”  
+- “Photosynthesis is the process by which green plants use sunlight to synthesize nutrients from carbon dioxide and water.”
+
+---
+
+## 🚀 Running the Example
+
+### 1. Requirements
+
+Make sure you have:
+
+- **Go 1.25+** installed  
+- Access to a **Google Gemini API key**  
+- Access to a **Milvus instance** (local or cloud)
+
+Verify your Go installation:
+
+```bash
+go version
+```
+If you don’t have Milvus running locally, you can start it quickly with Docker:
+```bash
+docker run -p 19530:19530 milvusdb/milvus:latest
+```
+### 2. Clone and Navigate
+```bash
+git clone https://github.com/tmc/langchaingo.git
+cd langchaingo/examples/googleai-milvus-rag-example
+```
+### 3. Set Environment Variables
+Linux / macOS
+```bash
+export GEMINI_API_KEY=your_gemini_api_key_here
+export MILVUS_URL=localhost:19530
+# Optional for Milvus Cloud
+export MILVUS_API_KEY=your_milvus_api_key_here
+```
+Window
+```bash
+$env:GEMINI_API_KEY="your_gemini_api_key_here"
+$env:MILVUS_URL="localhost:19530"
+$env:MILVUS_API_KEY="your_milvus_api_key_here"
+```
+### 4. Run the Program
+```bash
+go run main.go
+```
+### 5. Example Output
+```bash
+Answer: Machine learning is a branch of artificial intelligence that allows systems to learn from data and improve automatically through experience.
+```

examples/googleai-milvus-rag-example/go.mod

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+module github.com/tmc/langchaingo/examples/googleai-milvus-rag-example
+
+go 1.25.4
+
+require (
+	cloud.google.com/go v0.118.3 // indirect
+	cloud.google.com/go/ai v0.7.0 // indirect
+	cloud.google.com/go/aiplatform v1.74.0 // indirect
+	cloud.google.com/go/auth v0.15.0 // indirect
+	cloud.google.com/go/auth/oauth2adapt v0.2.7 // indirect
+	cloud.google.com/go/compute/metadata v0.6.0 // indirect
+	cloud.google.com/go/iam v1.4.1 // indirect
+	cloud.google.com/go/longrunning v0.6.4 // indirect
+	cloud.google.com/go/vertexai v0.12.0 // indirect
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/blang/semver/v4 v4.0.0 // indirect
+	github.com/cenkalti/backoff/v4 v4.3.0 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/cilium/ebpf v0.11.0 // indirect
+	github.com/cockroachdb/errors v1.9.1 // indirect
+	github.com/cockroachdb/logtags v0.0.0-20211118104740-dabe8e521a4f // indirect
+	github.com/cockroachdb/redact v1.1.3 // indirect
+	github.com/containerd/cgroups/v3 v3.0.3 // indirect
+	github.com/coreos/go-semver v0.3.0 // indirect
+	github.com/coreos/go-systemd/v22 v22.5.0 // indirect
+	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
+	github.com/dlclark/regexp2 v1.10.0 // indirect
+	github.com/docker/go-units v0.5.0 // indirect
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/form3tech-oss/jwt-go v3.2.3+incompatible // indirect
+	github.com/fxamacker/cbor/v2 v2.7.0 // indirect
+	github.com/getsentry/sentry-go v0.30.0 // indirect
+	github.com/go-logr/logr v1.4.3 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/go-ole/go-ole v1.3.0 // indirect
+	github.com/godbus/dbus/v5 v5.0.4 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/golang/protobuf v1.5.4 // indirect
+	github.com/google/btree v1.1.3 // indirect
+	github.com/google/generative-ai-go v0.15.1 // indirect
+	github.com/google/s2a-go v0.1.9 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/googleapis/enterprise-certificate-proxy v0.3.5 // indirect
+	github.com/googleapis/gax-go/v2 v2.14.1 // indirect
+	github.com/gorilla/websocket v1.5.0 // indirect
+	github.com/grpc-ecosystem/go-grpc-middleware v1.4.0 // indirect
+	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0 // indirect
+	github.com/grpc-ecosystem/grpc-gateway v1.16.0 // indirect
+	github.com/grpc-ecosystem/grpc-gateway/v2 v2.18.0 // indirect
+	github.com/jonboulle/clockwork v0.2.2 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/klauspost/compress v1.18.0 // indirect
+	github.com/kr/pretty v0.3.1 // indirect
+	github.com/kr/text v0.2.0 // indirect
+	github.com/lufia/plan9stats v0.0.0-20250317134145-8bc96cf8fc35 // indirect
+	github.com/milvus-io/milvus-proto/go-api/v2 v2.6.3 // indirect
+	github.com/milvus-io/milvus-sdk-go/v2 v2.4.0 // indirect
+	github.com/milvus-io/milvus/client/v2 v2.6.1 // indirect
+	github.com/milvus-io/milvus/pkg/v2 v2.6.3 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/opencontainers/runtime-spec v1.0.2 // indirect
+	github.com/panjf2000/ants/v2 v2.11.3 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	github.com/pkoukk/tiktoken-go v0.1.6 // indirect
+	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
+	github.com/power-devops/perfstat v0.0.0-20240221224432-82ca36839d55 // indirect
+	github.com/prometheus/client_golang v1.20.5 // indirect
+	github.com/prometheus/client_model v0.6.1 // indirect
+	github.com/prometheus/common v0.62.0 // indirect
+	github.com/prometheus/procfs v0.15.1 // indirect
+	github.com/rogpeppe/go-internal v1.13.1 // indirect
+	github.com/samber/lo v1.27.0 // indirect
+	github.com/shirou/gopsutil/v3 v3.24.5 // indirect
+	github.com/shoenig/go-m1cpu v0.1.6 // indirect
+	github.com/sirupsen/logrus v1.9.3 // indirect
+	github.com/soheilhy/cmux v0.1.5 // indirect
+	github.com/spaolacci/murmur3 v1.1.0 // indirect
+	github.com/spf13/cast v1.3.1 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
+	github.com/stretchr/testify v1.11.1 // indirect
+	github.com/tidwall/gjson v1.17.1 // indirect
+	github.com/tidwall/match v1.1.1 // indirect
+	github.com/tidwall/pretty v1.2.0 // indirect
+	github.com/tklauser/go-sysconf v0.3.15 // indirect
+	github.com/tklauser/numcpus v0.10.0 // indirect
+	github.com/tmc/grpc-websocket-proxy v0.0.0-20201229170055-e5319fda7802 // indirect
+	github.com/tmc/langchaingo v0.1.14 // indirect
+	github.com/uber/jaeger-client-go v2.30.0+incompatible // indirect
+	github.com/x448/float16 v0.8.4 // indirect
+	github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2 // indirect
+	github.com/yusufpapurcu/wmi v1.2.4 // indirect
+	go.etcd.io/bbolt v1.3.11 // indirect
+	go.etcd.io/etcd/api/v3 v3.5.5 // indirect
+	go.etcd.io/etcd/client/pkg/v3 v3.5.5 // indirect
+	go.etcd.io/etcd/client/v2 v2.305.5 // indirect
+	go.etcd.io/etcd/client/v3 v3.5.5 // indirect
+	go.etcd.io/etcd/pkg/v3 v3.5.5 // indirect
+	go.etcd.io/etcd/raft/v3 v3.5.5 // indirect
+	go.etcd.io/etcd/server/v3 v3.5.5 // indirect
+	go.opentelemetry.io/auto/sdk v1.1.0 // indirect
+	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.59.0 // indirect
+	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.61.0 // indirect
+	go.opentelemetry.io/otel v1.36.0 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.20.0 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.20.0 // indirect
+	go.opentelemetry.io/otel/metric v1.36.0 // indirect
+	go.opentelemetry.io/otel/sdk v1.36.0 // indirect
+	go.opentelemetry.io/otel/trace v1.36.0 // indirect
+	go.opentelemetry.io/proto/otlp v1.0.0 // indirect
+	go.uber.org/atomic v1.11.0 // indirect
+	go.uber.org/automaxprocs v1.5.3 // indirect
+	go.uber.org/multierr v1.11.0 // indirect
+	go.uber.org/zap v1.27.0 // indirect
+	golang.org/x/crypto v0.41.0 // indirect
+	golang.org/x/exp v0.0.0-20240808152545-0cdaa3abc0fa // indirect
+	golang.org/x/net v0.43.0 // indirect
+	golang.org/x/oauth2 v0.30.0 // indirect
+	golang.org/x/sync v0.16.0 // indirect
+	golang.org/x/sys v0.35.0 // indirect
+	golang.org/x/text v0.28.0 // indirect
+	golang.org/x/time v0.10.0 // indirect
+	google.golang.org/api v0.224.0 // indirect
+	google.golang.org/genproto v0.0.0-20250303144028-a0af3efb3deb // indirect
+	google.golang.org/genproto/googleapis/api v0.0.0-20250303144028-a0af3efb3deb // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20250227231956-55c901821b1e // indirect
+	google.golang.org/grpc v1.71.0 // indirect
+	google.golang.org/protobuf v1.36.5 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
+	gopkg.in/natefinch/lumberjack.v2 v2.2.1 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+	k8s.io/apimachinery v0.32.3 // indirect
+	sigs.k8s.io/yaml v1.4.0 // indirect
+)