Corrected the counting of the total number of items in the result list (#125)

Corrected the counting of the total number of items in the result list.

Author: mvanbrab

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fixed the broken production version due to a missing package (#123).
+- Corrected the counting of the total number of items in the result list (#120).
 
 ## [1.2.0] - 2024-05-07
 

cypress/e2e/total-items.cy.js

@@ -0,0 +1,8 @@
+describe("Total items", () => {
+  it("The total number of results must be correct, even if not all SPARQL query variables used in the WHERE clause are selected for display in the SELECT clause", () => {
+    cy.visit("/");
+    cy.contains("For testing only").click();
+    cy.contains("A test on counting the total number results").click();
+    cy.contains("1-10 of 20");
+  });
+});

public/queries/so_distinct.rq

@@ -0,0 +1,3 @@
+SELECT DISTINCT ?s ?o WHERE {
+  ?s ?p ?o
+}

src/config.json

@@ -279,6 +279,16 @@
           "http://localhost:8080/example/dup2"
         ]
       }
+    },
+    {
+      "id": "9050",
+      "queryGroupId": "c-tst",
+      "queryLocation": "so_distinct.rq",
+      "name": "A test on counting the total number results",
+      "description": "Query a source containing ?s ?p1 ?o and ?s ?p2 ?o with p1 != p2 and request only ?s ?o",
+      "comunicaContext": {
+        "sources": ["http://localhost:8080/example/dup1"]
+      }
     }
   ]
 }

src/dataProvider/SparqlDataProvider.js

@@ -35,10 +35,9 @@ configManager.on('configChanged', onConfigChanged);
 
 export default {
   getList: async function getList(resource, { pagination, sort, filter, meta }) {
-  
     const query = findQueryWithId(resource);
-    query.limit = pagination.perPage;
-    query.offset = (pagination.page - 1) * pagination.perPage;
+    const limit = pagination.perPage;
+    const offset = (pagination.page - 1) * pagination.perPage;
     query.sort = sort;
 
     handleComunicaContextCreation(query);
@@ -53,6 +52,8 @@ export default {
     }
 
     let results = await executeQuery(query);
+    let totalItems = results.length;
+    results = results.slice(offset, offset + limit);
 
     if (Object.keys(filter).length > 0) {
       results = results.filter((result) => {
@@ -64,7 +65,7 @@ export default {
 
     return {
       data: results,
-      total: query.totalItems
+      total: totalItems
     };
   },
   getOne: async function getOne() {
@@ -125,16 +126,6 @@ async function fetchQuery(query) {
     if (!query.variableOntology) {
       query.variableOntology = findPredicates(parsedQuery);
     }
-    if (parsedQuery.limit !== undefined && query.offset + query.limit > parsedQuery.limit) {
-      parsedQuery.limit = parsedQuery.limit - query.offset;
-    } else {
-      parsedQuery.limit = query.limit;
-    }
-    if (parsedQuery.offset) {
-      parsedQuery.offset += query.offset;
-    } else {
-      parsedQuery.offset = query.offset;
-    }
     if (!parsedQuery.order && query.sort && query.sort.field !== "id") {
       const { field, order } = query.sort;
       parsedQuery.order = [
@@ -290,7 +281,6 @@ async function handleQueryExecution(execution, query) {
     const resultType = execution.resultType;
     if (execution.resultType !== "boolean") {
       const metadata = await execution.metadata();
-      query.totalItems = await countQueryResults(query);
       variables = metadata.variables.map((val) => {
         return val.value;
       });
@@ -301,51 +291,6 @@ async function handleQueryExecution(execution, query) {
   }
 }
 
-/**
- * Predict the total number of elements in the result of a query
- * @param {object} query - the query element from the configuration
- * @returns {number} the actual number of results in the query, if it were executed
- */
-async function countQueryResults(query) {
-  const parser = new Parser();
-  const parsedQuery = parser.parse(query.rawText);
-  const distinctInitial = parsedQuery.distinct;
-  const offsetInitial = parsedQuery.offset;
-  const limitInitial = parsedQuery.limit;
-  parsedQuery.queryType = "SELECT";
-  parsedQuery.distinct = false;
-  parsedQuery.offset = 0;
-  if (parsedQuery.limit) {
-    delete parsedQuery.limit;
-  }
-  parsedQuery.variables = [
-    {
-      expression: {
-        type: "aggregate",
-        aggregation: "count",
-        expression: { termType: "Wildcard", value: "*" },
-        distinct: distinctInitial
-      },
-      variable: { termType: "Variable", value: "totalItems" },
-    },
-  ];
-  const generator = new Generator();
-  const countQuery = generator.stringify(parsedQuery);
-  const bindings = await myEngine.queryBindings(countQuery, {
-    sources: query.comunicaContext.sources,
-    fetch: fetch,
-    httpProxyHandler: proxyHandler,
-  });
-  let totalItems = parseInt((await bindings.toArray())[0].get("totalItems").value);
-  if (offsetInitial) {
-    totalItems -= offsetInitial;
-  }
-  if (limitInitial && totalItems > limitInitial) {
-    totalItems = limitInitial;
-  }
-  return totalItems;
-}
-
 const queryTypeHandlers = {
   bindings: configureBindingStream,
   quads: configureQuadStream,