prototypes/Decomposing classes like a boss.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Introduction\n",
    "\n",
    "In this blog post, I want to show you a graph-based way to split up a class into several independent ones. We take a small example class from Michael Feathers' book \"Working effectively with legacy code\" and use Neo4j's [Awesome Procedures On Cypher (APOC)](https://neo4j-contrib.github.io/neo4j-apoc-procedures).\n",
    "\n",
    "Hint: To run the notebook version of this blog post, you need to install the [ipython-cypher](https://ipython-cypher.readthedocs.io/en/latest/) extension."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```java\n",
    "class Reservation {\n",
    "\n",
    "    private int duration;\n",
    "    private int dailyRate;\n",
    "    private Date date;\n",
    "    private Customer customer;\n",
    "    private List fees = new ArrayList();\n",
    "\n",
    "    public Reservation(Customer customer, int duration, int dailyRate, Date date) {\n",
    "        this.customer = customer;\n",
    "        this.duration = duration;\n",
    "        this.dailyRate = dailyRate;\n",
    "        this.date = date;\n",
    "    }\n",
    "\n",
    "    public void extend(int additionalDays) {\n",
    "        duration += additionalDays;\n",
    "    }\n",
    "\n",
    "    public void extendForWeek() {\n",
    "        int weekRemainder = RentalCalendar.weekRemainderFor(date);\n",
    "        final int DAYS_PER_WEEK = 7;\n",
    "        extend(weekRemainder);\n",
    "        dailyRate = RateCalculator.computeWeekly(\n",
    "                customer.getRateCode()) / DAYS_PER_WEEK;\n",
    "    }\n",
    "\n",
    "    public void addFee(FeeRider rider) {\n",
    "        fees.add(rider);\n",
    "    }\n",
    "\n",
    "    int getAdditionalFees() {\n",
    "        int total = 0;\n",
    "        for (Iterator it = fees.iterator(); it.hasNext(); ) {\n",
    "            total += ((FeeRider) (it.next())).getAmount();\n",
    "\n",
    "        }\n",
    "        return total;\n",
    "    }\n",
    "\n",
    "    int getPrincipalFee() {\n",
    "        return dailyRate * RateCalculator.rateBase(customer) * duration;\n",
    "    }\n",
    "\n",
    "    public int getTotalFee() {\n",
    "        return getPrincipalFee() + getAdditionalFees();\n",
    "    }\n",
    "}\n",
    "\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 62,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "The cypher extension is already loaded. To reload it, use:\n",
      "  %reload_ext cypher\n"
     ]
    }
   ],
   "source": [
    "%load_ext cypher"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 63,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2 nodes deleted.\n",
      "24 relationship deleted.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[]"
      ]
     },
     "execution_count": 63,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH\n",
    "    ()-[u:USES]->(),\n",
    "    (n:NewClass)-[s:SHOULD_DECLARE]->()\n",
    "DELETE u,s,n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 64,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9 relationships created.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "        <th>method</th>\n",
       "        <th>relType</th>\n",
       "        <th>field</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getAdditionalFees</td>\n",
       "        <td>USES</td>\n",
       "        <td>fees</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>addFee</td>\n",
       "        <td>USES</td>\n",
       "        <td>fees</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getPrincipalFee</td>\n",
       "        <td>USES</td>\n",
       "        <td>customer</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>USES</td>\n",
       "        <td>customer</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getPrincipalFee</td>\n",
       "        <td>USES</td>\n",
       "        <td>duration</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extend</td>\n",
       "        <td>USES</td>\n",
       "        <td>duration</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extend</td>\n",
       "        <td>USES</td>\n",
       "        <td>duration</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>USES</td>\n",
       "        <td>date</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getPrincipalFee</td>\n",
       "        <td>USES</td>\n",
       "        <td>dailyRate</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>USES</td>\n",
       "        <td>dailyRate</td>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[['getAdditionalFees', 'USES', 'fees'],\n",
       " ['addFee', 'USES', 'fees'],\n",
       " ['getPrincipalFee', 'USES', 'customer'],\n",
       " ['extendForWeek', 'USES', 'customer'],\n",
       " ['getPrincipalFee', 'USES', 'duration'],\n",
       " ['extend', 'USES', 'duration'],\n",
       " ['extend', 'USES', 'duration'],\n",
       " ['extendForWeek', 'USES', 'date'],\n",
       " ['getPrincipalFee', 'USES', 'dailyRate'],\n",
       " ['extendForWeek', 'USES', 'dailyRate']]"
      ]
     },
     "execution_count": 64,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH\n",
    "    (c:Class {name : \"Reservation\"}),\n",
    "    (c)-[:DECLARES]->(m:Method),\n",
    "    (c)-[:DECLARES]->(f:Field),\n",
    "    (m)-[:READS|WRITES]->(f)\n",
    "WHERE NOT (m:Constructor)\n",
    "MERGE (m)-[u:USES]->(f)\n",
    "RETURN m.name as method, type(u) as relType, f.name as field"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 65,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3 relationships created.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "        <th>caller</th>\n",
       "        <th>relType</th>\n",
       "        <th>callee</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>USES</td>\n",
       "        <td>extend</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getTotalFee</td>\n",
       "        <td>USES</td>\n",
       "        <td>getPrincipalFee</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getTotalFee</td>\n",
       "        <td>USES</td>\n",
       "        <td>getAdditionalFees</td>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[['extendForWeek', 'USES', 'extend'],\n",
       " ['getTotalFee', 'USES', 'getPrincipalFee'],\n",
       " ['getTotalFee', 'USES', 'getAdditionalFees']]"
      ]
     },
     "execution_count": 65,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH\n",
    "    (c:Class {name : \"Reservation\"}),\n",
    "    (c)-[:DECLARES]->(m:Method),\n",
    "    (c)-[:DECLARES]->(m2:Method),\n",
    "    (m)-[:INVOKES]->(m2:Method)\n",
    "WHERE NOT (m:Constructor)\n",
    "MERGE (m)-[u:USES]->(m2)\n",
    "RETURN m.name as caller, type(u) as relType, m2.name as callee"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 66,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "6 properties set.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "        <th>method</th>\n",
       "        <th>weight</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getPrincipalFee</td>\n",
       "        <td>3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getAdditionalFees</td>\n",
       "        <td>1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getTotalFee</td>\n",
       "        <td>2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>4</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>addFee</td>\n",
       "        <td>1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extend</td>\n",
       "        <td>1</td>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[['getPrincipalFee', 3],\n",
       " ['getAdditionalFees', 1],\n",
       " ['getTotalFee', 2],\n",
       " ['extendForWeek', 4],\n",
       " ['addFee', 1],\n",
       " ['extend', 1]]"
      ]
     },
     "execution_count": 66,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH (m)-[u:USES]->(f)\n",
    "WITH m, COUNT(u) as weight\n",
    "SET m.weight = weight\n",
    "RETURN m.name as method, weight"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 67,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "5 properties set.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "        <th>field</th>\n",
       "        <th>weight</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>duration</td>\n",
       "        <td>2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>customer</td>\n",
       "        <td>2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>date</td>\n",
       "        <td>1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>fees</td>\n",
       "        <td>2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>dailyRate</td>\n",
       "        <td>2</td>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[['duration', 2], ['customer', 2], ['date', 1], ['fees', 2], ['dailyRate', 2]]"
      ]
     },
     "execution_count": 67,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH (m)-[u:USES]->(f:Field)\n",
    "WITH f, COUNT(u) as weight\n",
    "SET f.weight = weight\n",
    "RETURN f.name as field, weight"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 68,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3 properties set.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "        <th>callee</th>\n",
       "        <th>weight</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getPrincipalFee</td>\n",
       "        <td>1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getAdditionalFees</td>\n",
       "        <td>1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extend</td>\n",
       "        <td>1</td>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[['getPrincipalFee', 1], ['getAdditionalFees', 1], ['extend', 1]]"
      ]
     },
     "execution_count": 68,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH (m)-[u:USES]->(m2:Method)\n",
    "WITH m2, COUNT(u) as weight\n",
    "SET m2.weight = weight\n",
    "RETURN m2.name as callee, weight"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now we have to move the information of the called items to the relationship."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 69,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "12 properties set.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "        <th>count(r)</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>12</td>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[[12]]"
      ]
     },
     "execution_count": 69,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH (caller)-[r:USES]->(callee)\n",
    "SET r.weight = callee.weight\n",
    "RETURN count(r)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 70,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0 rows affected.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[]"
      ]
     },
     "execution_count": 70,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "CALL apoc.algo.community(25,null,'group','USES','OUTGOING','weight',10000)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 71,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "16 properties set.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "        <th>(n.name)</th>\n",
       "        <th>n.group</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>83</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getTotalFee</td>\n",
       "        <td>83</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>extend</td>\n",
       "        <td>83</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>getPrincipalFee</td>\n",
       "        <td>83</td>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[['extendForWeek', 83],\n",
       " ['getTotalFee', 83],\n",
       " ['extend', 83],\n",
       " ['getPrincipalFee', 83]]"
      ]
     },
     "execution_count": 71,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH (m:Method)-[:USES]->(f:Field)<-[:USES]-(m2:Method)\n",
    "WHERE m.group <> m2.group \n",
    "WITH m.group as newGroupId, m2.group as oldGroupId\n",
    "MATCH (n:Method) WHERE n.group = oldGroupId\n",
    "SET n.group = newGroupId+oldGroupId\n",
    "SET n.merged = true\n",
    "RETURN DISTINCT(n.name), n.group;"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 72,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0 rows affected.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "        <th>m.name</th>\n",
       "        <th>m.group</th>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[]"
      ]
     },
     "execution_count": 72,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH (m:Method)-[:USES]->(:Field)\n",
    "WHERE NOT EXISTS(m.merged)\n",
    "WITH m, m.group as groupId\n",
    "SET m.merged = false\n",
    "RETURN m.name, m.group;"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 73,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2 nodes created.\n",
      "2 properties set.\n",
      "12 relationships created.\n",
      "2 labels added.\n"
     ]
    },
    {
     "data": {
      "text/html": [
       "<table>\n",
       "    <tr>\n",
       "        <th>newClass</th>\n",
       "        <th>method</th>\n",
       "        <th>field</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>getTotalFee</td>\n",
       "        <td>getAdditionalFees</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>getTotalFee</td>\n",
       "        <td>getPrincipalFee</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>extend</td>\n",
       "        <td>duration</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>extend</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>customer</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>dailyRate</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>extendForWeek</td>\n",
       "        <td>date</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>45</td>\n",
       "        <td>addFee</td>\n",
       "        <td>fees</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>45</td>\n",
       "        <td>getAdditionalFees</td>\n",
       "        <td>fees</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>getPrincipalFee</td>\n",
       "        <td>duration</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>getPrincipalFee</td>\n",
       "        <td>customer</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "        <td>83</td>\n",
       "        <td>getPrincipalFee</td>\n",
       "        <td>dailyRate</td>\n",
       "    </tr>\n",
       "</table>"
      ],
      "text/plain": [
       "[[83, 'getTotalFee', 'getAdditionalFees'],\n",
       " [83, 'getTotalFee', 'getPrincipalFee'],\n",
       " [83, 'extend', 'duration'],\n",
       " [83, 'extendForWeek', 'extend'],\n",
       " [83, 'extendForWeek', 'customer'],\n",
       " [83, 'extendForWeek', 'dailyRate'],\n",
       " [83, 'extendForWeek', 'date'],\n",
       " [45, 'addFee', 'fees'],\n",
       " [45, 'getAdditionalFees', 'fees'],\n",
       " [83, 'getPrincipalFee', 'duration'],\n",
       " [83, 'getPrincipalFee', 'customer'],\n",
       " [83, 'getPrincipalFee', 'dailyRate']]"
      ]
     },
     "execution_count": 73,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%cypher\n",
    "MATCH (m:Method)-[:USES]->(f)\n",
    "WHERE (NOT EXISTS(m.merge) OR m.merge = False)\n",
    "MERGE (c:NewClass { name: m.group})\n",
    "MERGE (c)-[:SHOULD_DECLARE]->(m)\n",
    "MERGE (c)-[:SHOULD_DECLARE]->(f)\n",
    "RETURN c.name as newClass, m.name as method, f.name as field"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
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