在Parse中实现关系型连接查询的技术指南

8min
使用 Parse 的连接查询
介绍
在本指南中，您将执行 Parse 中的关系查询，模拟使用 NoSQL 数据库的 SQL JOIN 查询的行为。
先决条件
要完成本教程，您需要：
一个应用程序 在 Back4App 上创建.
目标
以 SQL JOIN 查询的方式查询存储在 Back4App 上的关系数据。
- 理解 Parse.Query 类
任何 Parse 查询操作都使用 Parse.Query 对象类型，这将帮助您在整个应用程序中从数据库中检索特定数据。重要的是要知道 Parse.Query 只有在调用检索方法（如 Parse.Query.find 或 Parse.Query.get）后才会解析，因此可以设置查询并在实际调用之前链接多个修饰符。
要创建一个新的 Parse.Query, 您需要将所需的 Parse.Object 子类作为参数传递，这将包含您的查询结果。下面可以看到一个示例查询，其中查询了一个虚构的 Profile 子类。
JS
 // This will create your query
 let parseQuery = new Parse.Query("Profile");
 // The query will resolve only after calling this method
 let queryResult = await parseQuery.find();
 // This will create your query
 let parseQuery = new Parse.Query("Profile");
 // The query will resolve only after calling this method
 let queryResult = await parseQuery.find();
﻿
您可以在 Parse.Query 类的 官方文档中了解更多信息。
- 在 Back4App 上保存一些数据
让我们创建两个示例类， TableA 和 TableB, 这将是我们在本指南中查询的目标。在 Parse JS 控制台中，可以直接运行 JavaScript 代码，使用 JS SDK 命令查询和更新您的应用程序数据库内容。从您的 JS 控制台运行下面的代码并在 Back4App 中插入数据。
以下是您的仪表板中 JS 控制台的样子：
﻿
继续创建以下内容的类：
JS
// Create TableA and its records
let TableARecord1 = new Parse.Object('TableA');
TableARecord1.set('FieldA', 'Value A 1');
TableARecord1 = await TableARecord1.save();

let TableARecord2 = new Parse.Object('TableA');
TableARecord2.set('FieldA', 'Value A 2');
TableARecord2 = await TableARecord2.save();

let TableARecord3 = new Parse.Object('TableA');
TableARecord3.set('FieldA', 'Value A 3');
TableARecord3 = await TableARecord3.save();

// Create TableB and its records, some of them linked to TableA
let TableBRecord1 = new Parse.Object('TableB');
TableBRecord1.set('FieldB', 'Value B 1');
TableBRecord1.set('link', TableARecord1);
TableBRecord1 = await TableBRecord1.save();

let TableBRecord2 = new Parse.Object('TableB');
TableBRecord2.set('FieldB', 'Value B 2');
TableBRecord2.set('link', TableARecord1);
TableBRecord2 = await TableBRecord2.save();

let TableBRecord3 = new Parse.Object('TableB');
TableBRecord3.set('FieldB', 'Value B 3');
TableBRecord3.set('link', TableARecord3);
TableBRecord3 = await TableBRecord3.save();

let TableBRecord4 = new Parse.Object('TableB');
TableBRecord4.set('FieldB', 'Value B 4');
TableBRecord4 = await TableBRecord4.save();

console.log('Success!');
// Create TableA and its records
let TableARecord1 = new Parse.Object('TableA');
TableARecord1.set('FieldA', 'Value A 1');
TableARecord1 = await TableARecord1.save();

let TableARecord2 = new Parse.Object('TableA');
TableARecord2.set('FieldA', 'Value A 2');
TableARecord2 = await TableARecord2.save();

let TableARecord3 = new Parse.Object('TableA');
TableARecord3.set('FieldA', 'Value A 3');
TableARecord3 = await TableARecord3.save();

// Create TableB and its records, some of them linked to TableA
let TableBRecord1 = new Parse.Object('TableB');
TableBRecord1.set('FieldB', 'Value B 1');
TableBRecord1.set('link', TableARecord1);
TableBRecord1 = await TableBRecord1.save();

let TableBRecord2 = new Parse.Object('TableB');
TableBRecord2.set('FieldB', 'Value B 2');
TableBRecord2.set('link', TableARecord1);
TableBRecord2 = await TableBRecord2.save();

let TableBRecord3 = new Parse.Object('TableB');
TableBRecord3.set('FieldB', 'Value B 3');
TableBRecord3.set('link', TableARecord3);
TableBRecord3 = await TableBRecord3.save();

let TableBRecord4 = new Parse.Object('TableB');
TableBRecord4.set('FieldB', 'Value B 4');
TableBRecord4 = await TableBRecord4.save();

console.log('Success!');
﻿
- 查询数据
现在您已经填充了类，我们可以在其中执行关系查询。让我们开始执行 INNER JOIN, 引入我们将在所有示例中使用的连接关系查询。此查询表示表 A 和表 B 之间两个组合查询的结果，返回所有通过特定条件相关的记录，使用 Parse.Query.matchesQuery 方法.
JS
// JOIN query, get all records in TableA that have matching records in TableB
let innerQueryTableA = new Parse.Query("TableA");
// Limit to 10 results only for example so we don't fetch too much data
innerQueryTableA.limit(10);
let joinQueryTableB = new Parse.Query("TableB");
// Match the TableA query by the "link" property
joinQueryTableB.matchesQuery("link", innerQueryTableA);
// Include the "link" property so we have the content of TableA as well
joinQueryTableB.include("link");
let joinQueryResults = await joinQueryTableB.find();

// INNER JOIN, get only the records in TableA that have matching records in TableB
console.log("INNER JOIN");
console.log("TABLE A ID | FIELD A | FIELD B");
for (let joinResult of joinQueryResults) {
 console.log(
   `${joinResult.get("link").id} | ${joinResult
     .get("link")
     .get("FieldA")} | ${joinResult.get("FieldB")}`
 );
}
// JOIN query, get all records in TableA that have matching records in TableB
let innerQueryTableA = new Parse.Query("TableA");
// Limit to 10 results only for example so we don't fetch too much data
innerQueryTableA.limit(10);
let joinQueryTableB = new Parse.Query("TableB");
// Match the TableA query by the "link" property
joinQueryTableB.matchesQuery("link", innerQueryTableA);
// Include the "link" property so we have the content of TableA as well
joinQueryTableB.include("link");
let joinQueryResults = await joinQueryTableB.find();

// INNER JOIN, get only the records in TableA that have matching records in TableB
console.log("INNER JOIN");
console.log("TABLE A ID | FIELD A | FIELD B");
for (let joinResult of joinQueryResults) {
 console.log(
   `${joinResult.get("link").id} | ${joinResult
     .get("link")
     .get("FieldA")} | ${joinResult.get("FieldB")}`
 );
}
﻿
该 INNER JOIN SQL 查询行为与我们通用的连接关系查询完全相同，因此我们需要在控制台中打印其结果。请记住，使用 Parse.Object，您可以使用 get 方法通过列名检索数据.
现在让我们执行一个 LEFT OUTER JOIN，获取所有在 TableA 中的记录，并在可用时显示 TableB 中的关系数据:
JS
// JOIN query, get all records in TableA that have matching records in TableB
let innerQueryTableA = new Parse.Query("TableA");
// Limit to 10 results only for example so we don't fetch too much data
innerQueryTableA.limit(10);
let joinQueryTableB = new Parse.Query("TableB");
// Match the TableA query by the "link" property
joinQueryTableB.matchesQuery("link", innerQueryTableA);
// Include the "link" property so we have the content of TableA as well
joinQueryTableB.include("link");
let joinQueryResults = await joinQueryTableB.find();

// LEFT OUTER JOIN, get records in TableA that have matching records in TableB and also every
// other TableA record
let queryTableA = new Parse.Query("TableA");
queryTableA.limit(10);
let queryTableAResults = await queryTableA.find();
console.log("LEFT JOIN");
console.log("TABLE A ID | FIELD A | FIELD B");
for (let result of queryTableAResults) {
 // Get all entries from JOIN query that have a link to this TableA entry
 let joinQueryResultsFiltered = joinQueryResults.filter(
   (joinQueryResult) =>
     joinQueryResult.get("link") !== undefined &&
     joinQueryResult.get("link").id == result.id
 );
 if (joinQueryResultsFiltered.length > 0) {
   for (let joinResult of joinQueryResultsFiltered) {
     let fieldBValue = joinResult.get("FieldB");
     console.log(`${result.id} | ${result.get("FieldA")} | ${fieldBValue}`);
   }
 } else {
   console.log(`${result.id} | ${result.get("FieldA")} | `);
 }
}
// JOIN query, get all records in TableA that have matching records in TableB
let innerQueryTableA = new Parse.Query("TableA");
// Limit to 10 results only for example so we don't fetch too much data
innerQueryTableA.limit(10);
let joinQueryTableB = new Parse.Query("TableB");
// Match the TableA query by the "link" property
joinQueryTableB.matchesQuery("link", innerQueryTableA);
// Include the "link" property so we have the content of TableA as well
joinQueryTableB.include("link");
let joinQueryResults = await joinQueryTableB.find();

// LEFT OUTER JOIN, get records in TableA that have matching records in TableB and also every
// other TableA record
let queryTableA = new Parse.Query("TableA");
queryTableA.limit(10);
let queryTableAResults = await queryTableA.find();
console.log("LEFT JOIN");
console.log("TABLE A ID | FIELD A | FIELD B");
for (let result of queryTableAResults) {
 // Get all entries from JOIN query that have a link to this TableA entry
 let joinQueryResultsFiltered = joinQueryResults.filter(
   (joinQueryResult) =>
     joinQueryResult.get("link") !== undefined &&
     joinQueryResult.get("link").id == result.id
 );
 if (joinQueryResultsFiltered.length > 0) {
   for (let joinResult of joinQueryResultsFiltered) {
     let fieldBValue = joinResult.get("FieldB");
     console.log(`${result.id} | ${result.get("FieldA")} | ${fieldBValue}`);
   }
 } else {
   console.log(`${result.id} | ${result.get("FieldA")} | `);
 }
}
﻿
右外连接RIGHT OUTER JOIN是左外连接的相反，获取来自TableB的记录。
MySQL
// JOIN query, get all records in TableA that have matching records in TableB
let innerQueryTableA = new Parse.Query("TableA");
// Limit to 10 results only for example so we don't fetch too much data
innerQueryTableA.limit(10);
let joinQueryTableB = new Parse.Query("TableB");
// Match the TableA query by the "link" property
joinQueryTableB.matchesQuery("link", innerQueryTableA);
// Include the "link" property so we have the content of TableA as well
joinQueryTableB.include("link");
let joinQueryResults = await joinQueryTableB.find();

// RIGHT OUTER JOIN, get records in TableA that have matching records in TableB and also every
// other TableB record
let queryTableB = new Parse.Query("TableB");
queryTableB.limit(10);
let queryTableBResults = await queryTableB.find();
console.log("RIGHT JOIN");
console.log("TABLE B ID | FIELD A | FIELD B");
for (let result of queryTableBResults) {
 // Get all entries from JOIN query that matches this TableB entry
 let joinQueryResultsFiltered = joinQueryResults.filter(
   (joinQueryResult) => joinQueryResult.id == result.id
 );
 if (joinQueryResultsFiltered.length > 0) {
   for (let joinResult of joinQueryResultsFiltered) {
     let fieldAValue = "";
     if (joinResult.get("link") !== undefined) {
       fieldAValue = joinResult.get("link").get("FieldA");
     }
     console.log(
       `${result.id} | ${fieldAValue} | ${joinResult.get("FieldB")}`
     );
   }
 } else {
   console.log(`${result.id} | | ${result.get("FieldB")}`);
 }
}
// JOIN query, get all records in TableA that have matching records in TableB
let innerQueryTableA = new Parse.Query("TableA");
// Limit to 10 results only for example so we don't fetch too much data
innerQueryTableA.limit(10);
let joinQueryTableB = new Parse.Query("TableB");
// Match the TableA query by the "link" property
joinQueryTableB.matchesQuery("link", innerQueryTableA);
// Include the "link" property so we have the content of TableA as well
joinQueryTableB.include("link");
let joinQueryResults = await joinQueryTableB.find();

// RIGHT OUTER JOIN, get records in TableA that have matching records in TableB and also every
// other TableB record
let queryTableB = new Parse.Query("TableB");
queryTableB.limit(10);
let queryTableBResults = await queryTableB.find();
console.log("RIGHT JOIN");
console.log("TABLE B ID | FIELD A | FIELD B");
for (let result of queryTableBResults) {
 // Get all entries from JOIN query that matches this TableB entry
 let joinQueryResultsFiltered = joinQueryResults.filter(
   (joinQueryResult) => joinQueryResult.id == result.id
 );
 if (joinQueryResultsFiltered.length > 0) {
   for (let joinResult of joinQueryResultsFiltered) {
     let fieldAValue = "";
     if (joinResult.get("link") !== undefined) {
       fieldAValue = joinResult.get("link").get("FieldA");
     }
     console.log(
       `${result.id} | ${fieldAValue} | ${joinResult.get("FieldB")}`
     );
   }
 } else {
   console.log(`${result.id} | | ${result.get("FieldB")}`);
 }
}
﻿
最后，我们有了完全外连接，这是左内连接和右内连接的组合：
MySQL
// JOIN query, get all records in TableA that have matching records in TableB
let innerQueryTableA = new Parse.Query("TableA");
// Limit to 10 results only for example so we don't fetch too much data
innerQueryTableA.limit(10);
let joinQueryTableB = new Parse.Query("TableB");
// Match the TableA query by the "link" property
joinQueryTableB.matchesQuery("link", innerQueryTableA);
// Include the "link" property so we have the content of TableA as well
joinQueryTableB.include("link");
let joinQueryResults = await joinQueryTableB.find();

// FULL OUTER JOIN, combining LEFT and RIGHT OUTER JOIN results
console.log("FULL JOIN");
console.log("TABLE ID | FIELD A | FIELD B");
// First print all INNER JOIN results
for (let joinResult of joinQueryResults) {
 console.log(
   `${joinResult.get("link").id} | ${joinResult
     .get("link")
     .get("FieldA")} | ${joinResult.get("FieldB")}`
 );
}
// Print LEFT JOIN leftovers
let outerQueryTableA = new Parse.Query("TableA");
outerQueryTableA.limit(10);
let outerQueryTableAResults = await outerQueryTableA.find();
// Get all entries from query that doesn't match the JOIN query results
let filteredOuterQueryTableAResults = outerQueryTableAResults.filter(
 (outerQueryTableAResult) =>
   joinQueryResults.find(
     (joinQueryResult) =>
       joinQueryResult.get("link") !== undefined &&
       joinQueryResult.get("link").id === outerQueryTableAResult.id
   ) === undefined
);
for (let result of filteredOuterQueryTableAResults) {
 console.log(`${result.id} | ${result.get("FieldA")} | `);
}
// Print RIGHT JOIN leftovers
let outerQueryTableB = new Parse.Query("TableB");
outerQueryTableB.limit(10);
let outerQueryTableBResults = await outerQueryTableB.find();
// Get all entries from query that doesn't match the JOIN query results
let filteredOuterQueryTableBResults = outerQueryTableBResults.filter(
 (outerQueryTableBResult) =>
   joinQueryResults.find(
     (joinQueryResult) => joinQueryResult.id === outerQueryTableBResult.id
   ) === undefined
);
for (let result of filteredOuterQueryTableBResults) {
 console.log(`${result.id} | | ${result.get("FieldB")}`);
}
// JOIN query, get all records in TableA that have matching records in TableB
let innerQueryTableA = new Parse.Query("TableA");
// Limit to 10 results only for example so we don't fetch too much data
innerQueryTableA.limit(10);
let joinQueryTableB = new Parse.Query("TableB");
// Match the TableA query by the "link" property
joinQueryTableB.matchesQuery("link", innerQueryTableA);
// Include the "link" property so we have the content of TableA as well
joinQueryTableB.include("link");
let joinQueryResults = await joinQueryTableB.find();

// FULL OUTER JOIN, combining LEFT and RIGHT OUTER JOIN results
console.log("FULL JOIN");
console.log("TABLE ID | FIELD A | FIELD B");
// First print all INNER JOIN results
for (let joinResult of joinQueryResults) {
 console.log(
   `${joinResult.get("link").id} | ${joinResult
     .get("link")
     .get("FieldA")} | ${joinResult.get("FieldB")}`
 );
}
// Print LEFT JOIN leftovers
let outerQueryTableA = new Parse.Query("TableA");
outerQueryTableA.limit(10);
let outerQueryTableAResults = await outerQueryTableA.find();
// Get all entries from query that doesn't match the JOIN query results
let filteredOuterQueryTableAResults = outerQueryTableAResults.filter(
 (outerQueryTableAResult) =>
   joinQueryResults.find(
     (joinQueryResult) =>
       joinQueryResult.get("link") !== undefined &&
       joinQueryResult.get("link").id === outerQueryTableAResult.id
   ) === undefined
);
for (let result of filteredOuterQueryTableAResults) {
 console.log(`${result.id} | ${result.get("FieldA")} | `);
}
// Print RIGHT JOIN leftovers
let outerQueryTableB = new Parse.Query("TableB");
outerQueryTableB.limit(10);
let outerQueryTableBResults = await outerQueryTableB.find();
// Get all entries from query that doesn't match the JOIN query results
let filteredOuterQueryTableBResults = outerQueryTableBResults.filter(
 (outerQueryTableBResult) =>
   joinQueryResults.find(
     (joinQueryResult) => joinQueryResult.id === outerQueryTableBResult.id
   ) === undefined
);
for (let result of filteredOuterQueryTableBResults) {
 console.log(`${result.id} | | ${result.get("FieldB")}`);
}
﻿
结论
在本指南的最后，您学习了如何使用 Parse 在 Back4App 上执行关系查询，并在 NoSQL 数据库中模拟最常见的 SQL JOIN 查询。
更新日期 27 Jan 2025
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在Parse中实现关系型连接查询的技术指南

使用 Parse 的连接查询

介绍

先决条件

目标

1 - 理解 Parse.Query 类

2 - 在 Back4App 上保存一些数据

3 - 查询数据

结论
