Avoid fetching from database when only accessing primary key

package.json

@@ -7,6 +7,7 @@
   "license": "WTFPL OR CC0-1.0",
   "dependencies": {
     "dataloader": "^2.2.2",
+    "db-errors": "^0.2.3",
     "match-value": "^1.1.0",
     "syncpipe": "^1.0.0"
   }

src/index.js

@@ -2,6 +2,8 @@
 
 const assert = require("assert");
 const matchValue = require("match-value");
+const dbErrors = require("db-errors");
+const DataLoader = require("dataloader");
 
 const knexIntrospect = require("./introspect");
 const dataloaderFromKnexResults = require("./dataloader-from-knex-results");
@@ -12,6 +14,14 @@ const dataloaderFromKnexResults = require("./dataloader-from-knex-results");
 - Update record: give each type an update method for that individual record, by ID? For "get previous value, then set new value" style usecases
 */
 
+async function wrapErrors(callback) {
+	try {
+		return callback();
+	} catch (error) {
+		throw dbErrors.wrapError(error);
+	}
+}
+
 function applyFilterPredicate(query, column, predicate, negate = false) {
 	if (predicate.__comparator === "not") {
 		return applyFilterPredicate(query, column, predicate.comparator, true);
@@ -85,8 +95,13 @@ module.exports = {
 		};
 	},
 	generateModule: async function generate(globalKnex, tableName, relations = {}) {
+		// Make sure we only look up each table once, even when resolving relations
+		let introspectLoader = new DataLoader((tables) => {
+			return Promise.all(tables.map((table) => knexIntrospect(globalKnex, table)));
+		});
+
 		// relations: { columnName: [ belongsTo, hasMany ] }, eg. on a posts table, it might have { thread_id: [ "thread", "posts" ] }
-		let tableLayout = await knexIntrospect(globalKnex, tableName);
+		let tableLayout = await introspectLoader.load(tableName);
 	
 		let fieldNames = Object.keys(tableLayout);
 		let primaryKeyColumn = Object.values(tableLayout).find((props) => props.isPrimaryKey === true);
@@ -111,8 +126,10 @@ module.exports = {
 			remoteTypes[remoteTypeName][remoteField] = async function(_, { $make, $getProperty, knex }) {
 				let tx = (knex ?? globalKnex);
 	
-				let result = await tx(tableName).columns("id").where({
+				let result = await wrapErrors(async () => {
-					[idFieldName]: await $getProperty(this, primaryKey)
+					return tx(tableName).columns("id").where({
+						[idFieldName]: await $getProperty(this, primaryKey)
+					});
 				});
 	
 				return result.map((item) => {
@@ -139,10 +156,15 @@ module.exports = {
 				types: {
 					[typeName]: async function({ id }) {
 						let normalFields = fieldNames.map((name) => {
-							return [ name, async (_, { dlayerKnexTable }) => {
+							if (name === primaryKey) {
-								let record = await dlayerKnexTable.load(id);
+								// No point making a trip to the database if all we need is an ID we already have
-								return record[name];
+								return [ name, id ];
-							}];
+							} else {
+								return [ name, async (_, { dlayerKnexTable }) => {
+									let record = await dlayerKnexTable.load(id);
+									return record[name];
+								}];
+							}
 						});
 	
 						let relationFields = [];
@@ -150,7 +172,7 @@ module.exports = {
 						for (let name of Object.keys(relations)) {
 							let localField = relations[name][0]; // eg. "thread"
 							let foreignKey = tableLayout[name].foreignKey;
-							let remoteTableLayout = await knexIntrospect(globalKnex, foreignKey.table);
+							let remoteTableLayout = await introspectLoader.load(foreignKey.table);
 	
 							if (remoteTableLayout[foreignKey.column].isPrimaryKey === true) {
 								let field = [ localField, async function (_, { $make, $getProperty }) {
@@ -188,7 +210,7 @@ module.exports = {
 					}
 	
 					if (orderBy != null) {
-						let ascending = orderBy.startsWith("-");
+						let ascending = !orderBy.startsWith("-");
 						
 						let orderField = (ascending === true)
 							? orderBy
@@ -205,7 +227,9 @@ module.exports = {
 						query = query.limit(limit);
 					}
 	
-					let result = await query;
+					let result = await wrapErrors(async () => {
+						return query;
+					});
 	
 					// TODO: Map result(s) to types
 					if (first === true) {
@@ -227,7 +251,9 @@ module.exports = {
 					let query = tx(tableName).delete();
 					query = applyFilterArgument(query, filter);
 	
-					let deletedRowCount = await query;
+					let deletedRowCount = await wrapErrors(async () => {
+						return query;
+					});
 	
 					return { count: deletedRowCount };
 				},
@@ -246,7 +272,9 @@ module.exports = {
 						applyFilterArgument(query, filter);
 					}
 	
-					let affected = await query;
+					let affected = await wrapErrors(async () => {
+						return query;
+					});
 	
 					return affected.map((item) => {
 						dlayerKnexTable.clear(item.id); // yeet from dataloader cache, so that we fetch the updated version instead
@@ -263,7 +291,9 @@ module.exports = {
 						.insert(values)
 						.returning("id");
 	
-					let result = await query;
+					let result = await wrapErrors(async () => {
+						return query;
+					});
 	
 					if (isArray) {
 						return result.map((item) => {

yarn.lock

@@ -12,6 +12,11 @@ dataloader@^2.2.2:
   resolved "https://registry.yarnpkg.com/dataloader/-/dataloader-2.2.2.tgz#216dc509b5abe39d43a9b9d97e6e5e473dfbe3e0"
   integrity sha512-8YnDaaf7N3k/q5HnTJVuzSyLETjoZjVmHc4AeKAzOvKHEFQKcn64OKBfzHYtE9zGjctNM7V9I0MfnUVLpi7M5g==
 
+db-errors@^0.2.3:
+  version "0.2.3"
+  resolved "https://registry.yarnpkg.com/db-errors/-/db-errors-0.2.3.tgz#a6a38952e00b20e790f2695a6446b3c65497ffa2"
+  integrity sha512-OOgqgDuCavHXjYSJoV2yGhv6SeG8nk42aoCSoyXLZUH7VwFG27rxbavU1z+VrZbZjphw5UkDQwUlD21MwZpUng==
+
 match-value@^1.1.0:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/match-value/-/match-value-1.1.0.tgz#ad311ef8bbe2d344a53ec3104e28fe221984b98e"