nim-ladybug/USAGE.md

Usage

This document is a quick guide for how to use this library. If you've cloned this repository, you can:

% nimble docs

... to auto-generate API docs -- unfortunately, with all the C wrappers, there's a lot and it's hard to know where to start.

Prior Reading

If you're just starting with Kuzu or graph databases, it's probably a good idea to familiarize yourself with the Kuzu Documentation and the Cypher Language. This library won't do much for you by itself without a basic understanding of Kuzu usage.

Checking Compatibility

This is a wrapper (with some additional niceties) for the system-installed Kuzu shared library. As such, the version of this library might not match with what you currently have installed.

Check the README, the History, and the following table to ensure you're using the correct version for your Kuzu installation. I'll make a modest effort for backwards compatibility, and other versions might work. Don't count too heavily on it. :-)

Kuzu Library Version	Nim Kuzu Version
v0.8.2	v0.1.0

You can use the kuzuVersionCompatible() function (along with the KUZU_VERSION and KUZU_LIBVERSION constants) to quickly check if things are looking right.

import kuzu

echo KUZU_VERSION            #=> "0.1.0"
echo KUZU_LIBVERSION         #=> "0.8.2"
echo kuzuVersionCompatible() #=> true

Connecting to a Database

Just call newKuzuDatabase(). Without an argument (or with an empty string), the database is in-memory. Any other argument is considered a filesystem path -- it will create an empty database if the path is currently non-existent, or open an existing database otherwise.

# "db" is in-memory and will evaporate when the process ends.
var db = newKuzuDatabase()

# "db" is persistent, stored in the directory "data".
var db = newKuzuDatabase("data")

The database path is retained, and can be recalled via db.path.

db.path #=> "data"

Database Configuration

The database is configured with default options by default. You can see them via:

echo $db.config
#=> (buffer_pool_size: 23371415552, max_num_threads: 16, ...

# Is compression enabled?
if db.config.enable_compression:
  echo "Yes!"

You can alter configuration options when connecting by passing a kuzuConfig object as the second argument to newKuzuDatabase():

# Open a readonly handle.
var db = newKuzuDatabase( "data", kuzuConfig( read_only=true ) )

The Connection

All interaction with the database is performed via a connection object. There are limitations to database handles and connection objects -- see the Kuzu Concurrency docs for details!

Call connect on an open database handle to create a new connection:

var conn = db.connect

You can set a maximum query lifetime, and interrupt any running queries (thread shutdown, ctrl-c, etc):

# Set a maximum ceiling on how long a query can run, in milliseconds.
conn.queryTimeout( 10 * 1000 ) # 10 seconds

# Cancel a running query.
conn.queryInterrupt()

Performing Queries

You can perform a basic query via the appropriately named query() function on the connection. Via this method, queries are run immediately. A KuzuQueryResult is returned - this is the object you'll be interacting with to see results.

A KuzuQueryResult can be turned into a string to quickly see the column headers and all tuple results:

var res = conn.query( """RETURN "Hello world", 1234, [1,2,3]""" )

echo $res #=>
# Hello world|1234|LIST_CREATION(1,2,3)
# Hello world|1234|[1,2,3]

Additionally, various query metadata is available for introspection:

var res = conn.query """
RETURN
  "Hello world" AS hi,
  1234 AS pin,
  [1,2,3] AS list
"""

assert res.num_columns == 3
assert res.num_tuples  == 1
echo res.compile_time   #=> 14.028
echo res.execution_time #=> 1.624

# Return the column names as a sequence.
assert res.column_names == @["hi", "pin", "list"]

# Return the column data types as a sequence.
assert res.column_types == @[KUZU_STRING, KUZU_INT64, KUZU_LIST]

Prepared Statements

If you're supplying an argument to a query, or you're running a query repeatedly, it's safer and faster to create a prepared statement via prepare() on the connection. These statements are only compiled once, and execution is deferred until you call execute().

var stmt = conn.prepare """
RETURN
  "Hello world" AS hi,
  1234 AS pin,
  [1,2,3] AS list
"""

# This returns a KuzuQueryResult, just like `conn.query()`.
var res = stmt.execute()

Arguments are labeled variables (prefixed with $) within the query. Parameters are matched by providing a Nim tuple argument to execute() - a simple round trip example:

var stmt = conn.prepare """
RETURN
  $message AS message,
  $digits AS digits,
  LIST_CREATION($list) AS list
"""

var res = stmt.execute( (message: "Hello", digits: 1234, list: "1,2,3") )

echo $res #=>
# message|digits|list
# Hello|1234|[1,2,3]

Type Conversion

When binding variables to a prepared statement, most Nim types are automatically converted to their respective Kuzu types.

var stmt = conn.prepare( """RETURN $num AS num""" )
var res  = stmt.execute( (num: 12) )

assert res.column_types[0] == KUZU_INT32

This might not necessarily be what you want - sometimes you'd rather be strict with typing, and you might be inserting into a column that has a different type than the default.

You can use integer type suffixes, or casting to be explicit as usual:

var stmt = conn.prepare( """RETURN $num AS num""" )
var res: KuzuQueryResult

res = stmt.execute( (num: 12'u64) )
assert res.column_types[0] == KUZU_UINT64

res = stmt.execute( (num: 12.float) )
assert res.column_types[0] == KUZU_DOUBLE

Kuzu Specific Types

In the example above, you may have noticed the LIST_CREATION($list) in the prepared query, and that we passed a string 1,2,3 as the $list parameter.

This is a useful way to easily use most Kuzu types without needing corresponding Nim ones -- if you're inserting into a table that is using a custom type, you can cast it using the query itself during insertion!

This has the additional advantage of letting Kuzu error check the validity of the content, and it works with the majority of types.

An extended example:

import std/sequtils
import kuzu

var db   = newKuzuDatabase()
var conn = db.connect

var res: KuzuQueryResult

# Create a node table.
#
res = conn.query """
CREATE NODE TABLE Example (
  id SERIAL,
  num UINT8,
  done BOOL,
  comment STRING,
  karma DOUBLE,
  thing UUID,
  created DATE,
  activity TIMESTAMP,
  PRIMARY KEY(id)
)
"""

# Prepare a statement for adding a node.
#
var stmt = conn.prepare """
CREATE (e:Example {
  num: $num,
  done: $done,
  comment: $comment,
  karma: $karma,
  thing: UUID($thing),
  created: DATE($created),
  activity: TIMESTAMP($activity)
})
"""

# Add a node row that contains specific Kuzu types.
#
res = stmt.execute((
  num: 2,
  done: true,
  comment: "Types!",
  karma: 16.7,
  thing: "e0e7232e-bec9-4625-9822-9d1a31ea6f93",
  created: "2025-03-29",
  activity: "2025-03-29"
))

# Show the current contents.
res = conn.query( """MATCH (e:Example) RETURN e.*""" )
echo $res #=>
# e.id|e.num|e.done|e.comment|e.karma|e.thing|e.created|e.activity
# 0|2|True|Types!|16.700000|e0e7232e-bec9-4625-9822-9d1a31ea6f93|2025-03-29|2025-03-29 00:00:00

# Show column names and their Kuzu types.
for pair in res.column_names.zip( res.column_types ):
  echo pair #=>
  # ("e.id", KUZU_SERIAL)
  # ("e.num", KUZU_UINT8)
  # ("e.done", KUZU_BOOL)
  # ("e.comment", KUZU_STRING)
  # ("e.karma", KUZU_DOUBLE)
  # ("e.thing", KUZU_UUID)
  # ("e.created", KUZU_DATE)
  # ("e.activity", KUZU_TIMESTAMP)

Reading Result Sets

So far we've just been showing values by converting the entire KuzuQueryResult to a string. Convenient for quick examples and debugging, but not much else.

A KuzuQueryResult is an iterator. You can use regular Nim functions that yield each KuzuFlatTuple -- essentially, each row that was returned in the set.

var res = conn.query """
  UNWIND [1,2,3] AS items
  UNWIND ["thing"] AS thing
  RETURN items, thing
"""

# KuzuFlatTuple can be stringified just like the result set.
for row in res:
  echo row #=>
  # 1|thing
  # 2|thing
  # 3|thing

Once iteration has reached the end, it is automatically rewound for reuse.

You can manually get the next KuzuFlatTuple via getNext(). Calling getNext() after the last row results in an error. Use hasNext() to check before calling.

var res = conn.query """
  UNWIND [1,2,3] AS items
  RETURN items
"""

# Get the first row.
if res.hasNext:
  var row = res.getNext
  echo row #=> 1

echo res.getNext #=> 2
echo res.getNext #=> 3
echo res.getNext #=> KuzuIndexError exception!

Manually rewind the KuzuQueryResult via rewind().

Working with Values

A KuzuFlatTuple contains the entire row. You can index a value at its column position, returning a KuzuValue.

var res = conn.query """
RETURN
  1 AS num,
  true AS done,
  "A comment" AS comment,
  12.84 AS karma,
  UUID("b41deae0-dddf-430b-981d-3fb93823e495") AS thing,
  DATE("2025-03-29") AS created
"""

var row = res.getNext

for idx in ( 0 .. res.num_columns-1 ):
  var value = row[idx]
  echo res.column_names[idx], ": ", value, " (", value.kind, ")" #=>
  # num: 1 (KUZU_INT64)
  # done: True (KUZU_BOOL)
  # comment: A comment (KUZU_STRING)
  # karma: 12.840000 (KUZU_DOUBLE)
  # thing: b41deae0-dddf-430b-981d-3fb93823e495 (KUZU_UUID)
  # created: 2025-03-29 (KUZU_DATE)

Types

A KuzuValue can always be stringified, irrespective of its Kuzu type. You can check what type it is via the 'kind' property.

var res = conn.query """RETURN "hello""""
var value = res.getNext[0]

assert value.kind == KUZU_STRING

A KuzuValue has conversion methods for Nim base types. You'll likely want to convert it for regular Nim usage:

var res = conn.query( "RETURN 2560" )
var value = res.getNext[0]

echo value + 1 #=> Type error!

assert $value == "2560"
assert value.toInt64 + 1 == 2561

Lists

A KuzuValue of type KUZU_LIST can be converted to a Nim sequence of KuzuValues with the toList() function:

import std/sequtils
import kuzu

var res = conn.query """
RETURN [10, 20, 30]
"""

var value = res.getNext[0]

var list = value.toList
echo list #=> @[10,20,30]

echo list.map( func(v:KuzuValue): int = v.toInt64 * 10 ) #=> @[100,200,300]

Struct-like Objects

Various Kuzu types can act like a struct - this includes KUZU_NODE, KUZU_REL, and of course an explicit KUZU_STRUCT itself, among others.

Convert a KuzuValue to a KuzuStructValue with toStruct(). For convenience, this is also aliased to toNode() and toRel().

Once converted, you can access struct values by passing the key name to []:

var res = conn.query """
RETURN {movie: "The Fifth Element", year: 1997}
"""

var value = res.getNext[0]

var struct = value.toStruct
echo struct["movie"], " was released in ", struct["year"], "." #=>
# "The Fifth Element was released in 1997."

Here's a more elaborate example, following a node path:

import
  std/sequtils,
  std/strformat
import kuzu

var db   = newKuzuDatabase()
var conn = db.connect

var res = conn.query """
  CREATE NODE TABLE Person (
    id SERIAL,
    name STRING, PRIMARY KEY (id)
  );
  CREATE REL TABLE Knows (
    FROM Person TO Person,
    since INT
  );

  CREATE (p:Person {name: "Bob"});
  CREATE (p:Person {name: "Alice"});
  CREATE (p:Person {name: "Bruce"});
  CREATE (p:Person {name: "Tom"});

  CREATE (a:Person {name: "Bruce"})-[r:Knows {since: 1997}]->(b:Person {name: "Tom"});
  CREATE (a:Person {name: "Bob"})-[r:Knows {since: 2009}]->(b:Person {name: "Alice"});
  CREATE (a:Person {name: "Alice"})-[r:Knows {since: 2010}]->(b:Person {name: "Bob"});
  CREATE (a:Person {name: "Bob"})-[r:Knows {since: 2003}]->(b:Person {name: "Bruce"});
"""

res = conn.query """
  MATCH path = (a:Person)-[r:Knows]->(b:Person)
  WHERE r.since > 2000
  RETURN r.since as Since, nodes(path) as People
  ORDER BY r.since
"""

# Who knows who since when?
#
for row in res:
  var since  = row[0]
  var people = row[1].toList.map( proc(p:KuzuValue):KuzuStructValue = p.toNode )
  echo &"""{people[0]["name"]} has known {people[1]["name"]} since {since}."""