Relationales Schema

dieser leitfaden erklärt, wie man mit relationalen schemata auf back4app arbeitet, einschließlich der erstellung verwandter klassen und der durchführung effizienter abfragen mit parse server sie werden lernen, wie man zeiger und beziehungen effektiv nutzt, zusammen mit praktischen beispielen was ist ein relationales schema? ein relationales schema organisiert daten in verschiedene klassen, die miteinander verbunden sind in parse server werden diese beziehungen verwaltet durch zeiger verweisen direkt auf ein einzelnes objekt beziehungen verwalten mehrerer verbindungen (viele zu viele beziehungen) diese werkzeuge ermöglichen es ihnen, komplexe abfragen effizient und konsistent durchzuführen ziele am ende dieses leitfadens werden sie in der lage sein beziehungen zwischen klassen mit zeigern und beziehungen zu erstellen relationale abfragen durchzuführen, um verbundene daten abzurufen ihr schema für bessere leistung zu optimieren voraussetzungen eine back4app anwendung erstellen sie eine app anleitung https //www back4app com/docs/get started/new parse app parse sdk installiert installationsanleitung https //www back4app com/docs/get started/parse sdk 1 erstellen verwandter klassen praktisches beispiel staaten und städte stellen sie sich vor, sie möchten ein system modellieren, in dem städte mit staaten verbunden sind klasse staat mit dem feld state name klasse stadt mit dem feld city name und einem pointer zu staat klassen und beziehungen erstellen javascript async function createstateandcity() { try { // create a state const state = parse object extend('state'); const california = new state(); california set('state name', 'california'); const savedstate = await california save(); console log(`state created with objectid ${savedstate id}`); // create a city with a pointer to state const city = parse object extend('city'); const losangeles = new city(); losangeles set('city name', 'los angeles'); losangeles set('state', savedstate); const savedcity = await losangeles save(); console log(`city created with objectid ${savedcity id}`); } catch (error) { console error('error creating state and city ', error message); } } createstateandcity(); flutter future\<void> createclasses() async { await parse() initialize('your app id', 'https //parseapi back4app com/', clientkey 'your client key', autosendsessionid true); // create a state final state = parseobject('state') set('state name', 'california'); final stateresult = await state save(); if (stateresult success) { // create a city with a pointer to state final city = parseobject('city') set('city name', 'los angeles') set('state', state); final cityresult = await city save(); if (cityresult success) { print('state and city created successfully '); } } } android public class mainactivity extends appcompatactivity { @override protected void oncreate(bundle savedinstancestate) { super oncreate(savedinstancestate); setcontentview(r layout activity main); // initialize parse parse initialize(new parse configuration builder(this) applicationid("your app id") clientkey("your client key") server("https //parseapi back4app com/") build() ); // create state and city createclasses(); } private void createclasses() { // create a state parseobject state = new parseobject("state"); state put("state name", "california"); state saveinbackground(e > { if (e == null) { log d("parse", "state created successfully with objectid " + state getobjectid()); // save city with a pointer to state parseobject city = new parseobject("city"); city put("city name", "los angeles"); city put("state", state); city saveinbackground(ex > { if (ex == null) { log d("parse", "city created successfully with objectid " + city getobjectid()); } else { log e("parse", "failed to create city " + ex getmessage()); } }); } else { log e("parse", "failed to create state " + e getmessage()); } }); } } ios struct state parseobject { var objectid string? var state name string? var createdat date? var updatedat date? } struct city parseobject { var objectid string? var city name string? var state state? var createdat date? var updatedat date? } func createclasses() async throws { try await parseswift initialize(applicationid "your app id", clientkey "your client key", serverurl url(string "https //parseapi back4app com")!) let state = state(state name "california") let savedstate = try await state save() var city = city(city name "los angeles", state savedstate) city = try await city save() print("state and city created successfully ") } php require 'vendor/autoload php'; use parse\parseclient; use parse\parseobject; parseclient initialize('your app id', 'your client key', 'https //parseapi back4app com/'); try { // create a state $state = new parseobject("state"); $state >set("state name", "california"); $state >save(); // create a city with a pointer to state $city = new parseobject("city"); $city >set("city name", "los angeles"); $city >set("state", $state); $city >save(); echo "state and city created successfully "; } catch (exception $ex) { echo "error " $ex >getmessage(); } net namespace parseexampleapp { class program { static async task main(string\[] args) { // initialize parse parseclient initialize(new parseclient configuration { applicationid = "your app id", server = "https //parseapi back4app com/", key = "your client key" }); // call the method to create state and city await createclassesasync(); } static async task createclassesasync() { try { // create a state var state = new parseobject("state"); state\["state name"] = "california"; await state saveasync(); console writeline($"state created with objectid {state objectid}"); // create a city with a pointer to the state var city = new parseobject("city"); city\["city name"] = "los angeles"; city\["state"] = state; // set the pointer to the state await city saveasync(); console writeline($"city created with objectid {city objectid}"); } catch (exception ex) { console writeline($"error {ex message}"); } } } } rest api # create state curl x post \\ h "x parse application id your app id" \\ h "x parse rest api key your rest api key" \\ h "content type application/json" \\ d '{"state name" "california"}' \\ https //parseapi back4app com/classes/state \# use the objectid of the created state to create a city curl x post \\ h "x parse application id your app id" \\ h "x parse rest api key your rest api key" \\ h "content type application/json" \\ d '{"city name" "los angeles", "state" {" type" "pointer", "classname" "state", "objectid" "state object id"}}' \\ https //parseapi back4app com/classes/city 2 abfragen verwandter daten jetzt, da die daten miteinander verbunden sind, können sie abfragen durchführen, um sie abzurufen beispiel 1 städte in einem bestimmten bundesstaat abrufen javascript const statequery = new parse query("state"); statequery equalto("state name", "california"); statequery first() then(state => { const cityquery = new parse query("city"); cityquery equalto("state", state); return cityquery find(); }) then(cities => { cities foreach(city => { console log(`city ${city get("city name")}`); }); }) catch(error => { console error("error fetching cities ", error message); }); flutter final statequery = querybuilder(parseobject('state')) whereequalto('state name', 'california'); final stateresult = await statequery query(); if (stateresult success && stateresult results != null) { final state = stateresult results! first; final cityquery = querybuilder(parseobject('city')) whereequalto('state', state); final cityresult = await cityquery query(); if (cityresult success && cityresult results != null) { for (var city in cityresult results!) { print('city ${city get\<string>('city name')}'); } } } android parsequery\<parseobject> statequery = parsequery getquery("state"); statequery whereequalto("state name", "california"); statequery getfirstinbackground((state, e) > { if (e == null) { parsequery\<parseobject> cityquery = parsequery getquery("city"); cityquery whereequalto("state", state); cityquery findinbackground((cities, ex) > { if (ex == null) { for (parseobject city cities) { log d("parse", "city " + city getstring("city name")); } } else { log e("parse", "error fetching cities " + ex getmessage()); } }); } else { log e("parse", "error fetching state " + e getmessage()); } }); ios let statequery = state query("state name" == "california") statequery first { result in switch result { case success(let state) let cityquery = city query("state" == state) cityquery find { cityresult in switch cityresult { case success(let cities) cities foreach { city in print("city \\(city city name ?? "unknown")") } case failure(let error) print("error fetching cities \\(error localizeddescription)") } } case failure(let error) print("error fetching state \\(error localizeddescription)") } } php use parse\parsequery; // query state $statequery = new parsequery("state"); $statequery >equalto("state name", "california"); $state = $statequery >first(); if ($state) { // query cities $cityquery = new parsequery("city"); $cityquery >equalto("state", $state); $cities = $cityquery >find(); foreach ($cities as $city) { echo "city " $city >get("city name") "\n"; } } net var statequery = new parsequery\<parseobject>("state") whereequalto("state name", "california"); var state = await statequery firstasync(); if (state != null) { var cityquery = new parsequery\<parseobject>("city") whereequalto("state", state); var cities = await cityquery findasync(); foreach (var city in cities) { console writeline($"city {city\["city name"]}"); } } rest api # query state curl x get \\ h "x parse application id your app id" \\ h "x parse rest api key your rest api key" \\ "https //parseapi back4app com/classes/state?where={\\"state name\\" \\"california\\"}" \# query cities \# replace state object id with the objectid from the state query curl x get \\ h "x parse application id your app id" \\ h "x parse rest api key your rest api key" \\ "https //parseapi back4app com/classes/city?where={\\"state\\" {\\" type\\" \\"pointer\\",\\"classname\\" \\"state\\",\\"objectid\\" \\"state object id\\"}}" beispiel 2 abfrage von staaten mit verwandten städten erstellen sie eine abfrage, die bundesstaaten zurückgibt, die mit einer stadt verbunden sind javascript const statequery = new parse query("state"); const cityquery = new parse query("city"); cityquery matchesquery("state", statequery); cityquery include("state"); cityquery find() then(cities => { cities foreach(city => { const state = city get("state"); console log(`city ${city get("city name")} belongs to state ${state get("state name")}`); }); }) catch(error => { console error("error fetching data ", error message); }); flutter final statequery = querybuilder(parseobject('state')); final cityquery = querybuilder(parseobject('city')) wherematchesquery('state', statequery) includeobject(\['state']); final cityresult = await cityquery query(); if (cityresult success && cityresult results != null) { for (var city in cityresult results!) { final state = city get\<parseobject>('state'); print('city ${city get\<string>('city name')} belongs to state ${state? get\<string>('state name')}'); } } android parsequery\<parseobject> statequery = parsequery getquery("state"); parsequery\<parseobject> cityquery = parsequery getquery("city"); cityquery wherematchesquery("state", statequery); cityquery include("state"); cityquery findinbackground((cities, e) > { if (e == null) { for (parseobject city cities) { parseobject state = city getparseobject("state"); log d("parse", "city " + city getstring("city name") + " belongs to state " + state getstring("state name")); } } else { log e("parse", "error " + e getmessage()); } }); ios let statequery = state query() let cityquery = city query(matchesquery(key "state", query statequery)) cityquery include("state") cityquery find { result in switch result { case success(let cities) cities foreach { city in if let state = city state { print("city \\(city city name ?? "unknown") belongs to state \\(state state name ?? "unknown")") } } case failure(let error) print("error \\(error localizeddescription)") } } php use parse\parsequery; $statequery = new parsequery("state"); $cityquery = new parsequery("city"); $cityquery >matchesquery("state", $statequery); $cityquery >includekey("state"); $cities = $cityquery >find(); foreach ($cities as $city) { $state = $city >get("state"); echo "city " $city >get("city name") " belongs to state " $state >get("state name") "\n"; } net var statequery = new parsequery\<parseobject>("state"); var cityquery = new parsequery\<parseobject>("city") wherematchesquery("state", statequery) include("state"); var cities = await cityquery findasync(); foreach (var city in cities) { var state = city get\<parseobject>("state"); console writeline($"city {city\["city name"]} belongs to state {state\["state name"]}"); } rest api curl x get \\ h "x parse application id your app id" \\ h "x parse rest api key your rest api key" \\ "https //parseapi back4app com/classes/city?where={\\"state\\" {\\"$inquery\\" {\\"classname\\" \\"state\\"}}}\&include=state" best practices um effektiv mit relationalen schemata unter verwendung von parse server in back4app zu arbeiten, befolgen sie diese best practices, um leistung, wartbarkeit und skalierbarkeit sicherzustellen wählen sie den richtigen beziehungstyp verwenden sie zeiger für eins zu eins beziehungen , wie das verknüpfen eines benutzers mit seinem profil verwenden sie beziehungen für viele zu viele beziehungen , wie das verknüpfen eines projekts mit mehreren aufgaben effiziente abfragen verwenden sie include() um verwandte daten in derselben abfrage zu laden, wodurch die notwendigkeit mehrerer anfragen verringert wird ergebnisse einschränken mit limit() und skip() um zu vermeiden, dass große datensätze auf einmal abgerufen werden häufig abgefragte felder indizieren um die suche zu beschleunigen übermäßige verschachtelung vermeiden halten sie abfragen flach um die komplexität zu reduzieren und die leistung zu verbessern verwenden sie verschachtelte abfragen sparsam und nur wenn nötig komplexe abfragen an cloud code auslagern für komplexe abfragen mit mehreren beziehungen oder großen datensätzen, lagern sie diese an cloud code aus, um den client leicht und reaktionsschnell zu halten fazit in diesem leitfaden haben sie gelernt, wie man beziehungen zwischen klassen erstellt und verwandte objekte auf back4app abfragt erkunden sie weiter die spezifische sdk dokumentation https //docs parseplatform org um noch tiefer einzutauchen!