open DB created by foreign language in raw mode by default (#128)

* open DB created by foreign language in raw mode by default

* adds guide to open DB by foreign language in README and doc

Author: Congyuwang

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "RocksDict"
-version = "0.3.24-beta.1"
+version = "0.3.24-beta.2"
 edition = "2021"
 description = "Rocksdb Python Binding"
 
@@ -10,6 +10,11 @@ description = "Rocksdb Python Binding"
 name = "rocksdict"
 crate-type = ["cdylib"]
 
+[[bin]]
+name = "create_cf_db"
+path = "bin/create-cf-db/main.rs"
+test = false
+
 [dependencies]
 rocksdb = { path = "rust-rocksdb" }
 librocksdb-sys = { path = "rust-rocksdb/librocksdb-sys" }

README.md

@@ -29,6 +29,32 @@ These two purposes operate in different modes:
 - **Raw mode** (`options=Options(raw_mode=True)`),
   which allows storing only `bytes`.
 
+## Easily inspect RocksDB created by C++, Java, or Other Languages
+
+```python
+from rocksdict import Rdict
+
+# This will automatically load latest options and column families.
+# Note also that this is automatically RAW MODE,
+# as it knows that the db is not created by RocksDict.
+db = Rdict("db_path")
+
+# list column families
+cfs = Rdict.list_cf("db_path")
+print(cfs)
+
+# use one of the column families
+cf1 = db.get_column_family(cfs[1])
+
+# iterate through all key-value pairs in cf1
+for k, v in cf1.items():
+    print(f"{k} -> {v}")
+
+# iterate through all wide columns in cf1
+for k, v in cf1.entities():
+    print(f"{k} -> {v}")
+```
+
 ## Examples
 
 ### A minimal example

bin/create-cf-db/main.rs

@@ -0,0 +1,17 @@
+//! for convenient testing purpose
+use rocksdb::{Options, DB};
+use std::env::args;
+
+fn main() {
+    let args = args().collect::<Vec<_>>();
+    if args.len() < 3 {
+        println!("usage: ./create_cf_db path cf1 cf2 cf3...");
+        return;
+    }
+
+    let path = &args[1];
+    let mut opts = Options::default();
+    opts.create_if_missing(true);
+    opts.create_missing_column_families(true);
+    DB::open_cf(&opts, path, &args[2..]).expect("failed to create db");
+}