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query-step.ts
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query-step.ts
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import object_hash from "object-hash";
import Query from "./query";
import negate_stage from "./negate-stage";
import QueryStage from "./query-stage";
export default abstract class QueryStep {
body: any;
hash() {
return QueryStep.hashBody(this.body);
}
static fromStage(stage: QueryStage, unwind = true) {
if (stage.$lookup) {
const clonedStageBody = Object.assign({}, stage.$lookup);
clonedStageBody.unwind = unwind;
return [new Lookup(clonedStageBody)];
} else if (stage.$match) {
return Object.keys(stage.$match).map(
(field) => new Match({ [field]: stage.$match[field] })
);
}
throw new Error("Unsupported stage: " + JSON.stringify(stage));
}
pushDump(dumps: Query[]) {
dumps.push(this.body);
return dumps;
}
static hashBody(body: any) {
return object_hash(body, {
algorithm: "md5",
excludeKeys: (key) => key === "as",
});
}
abstract getUsedFields(): string[];
abstract getCost(): number;
abstract pushStage(pipeline: any[]): any[];
abstract negate(): QueryStep;
}
export type LookupBody = {
from: string;
localField: string;
foreignField: string;
as?: string;
unwind?: boolean;
};
export class Lookup extends QueryStep {
unwind: boolean;
body: LookupBody;
constructor(body: LookupBody) {
super();
const cleared_body: LookupBody = {
from: body.from,
localField: body.localField,
foreignField: body.foreignField,
as: "temp", //overwritten below, included for type safety
};
cleared_body.as = QueryStep.hashBody(cleared_body);
this.body = cleared_body;
this.unwind = body.unwind || false;
}
hash() {
if (!this.body.as) {
throw new Error(
"Cannot hash a lookup step without an `as` property"
);
}
return this.body.as;
}
pushStage(pipeline: any[]) {
pipeline.push({ $lookup: this.body });
if (this.unwind) {
pipeline.push({ $unwind: "$" + this.body.as });
}
return pipeline;
}
getUsedFields() {
return this.body.localField.split(".");
}
getCost() {
return 8;
}
negate() {
return this;
}
}
export class Match extends QueryStep {
constructor(body: any) {
super();
this.body = body;
}
pushStage(pipeline: any[]) {
pipeline.push({ $match: this.body });
return pipeline;
}
getUsedFields() {
return getAllKeys(this.body)
.map((path) => path.split("."))
.reduce((acc, fields) =>
acc.concat(fields.filter((field) => !field.startsWith("$")))
);
}
getCost() {
return this.body.$or ? 2 : 0;
}
negate() {
return new Match(negate_stage(this.body));
}
}
function getAllKeys(obj: any): string[] {
return Object.keys(obj).reduce((acc, key) => {
if (obj[key] instanceof Object) {
acc.push(...getAllKeys(obj[key]));
}
if (!Array.isArray(obj)) {
acc.push(key);
}
return acc;
}, [] as string[]);
}

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