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query-step.js
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query-step.js
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const object_hash = require("object-hash");
const negate_stage = require("./negate_stage.js");
class QueryStep {
constructor(body) {
this.body = body;
}
hash() {
return QueryStep.hashBody(this.body);
}
static fromStage(stage, unwind = true) {
if (stage.$lookup) {
const clonedStageBody = Object.assign({}, stage.$lookup);
clonedStageBody.unwind = unwind;
return [new QueryStep.Lookup(clonedStageBody)];
} else if (stage.$match) {
return Object.keys(stage.$match).map(
field => new QueryStep.Match({ [field]: stage.$match[field] })
);
}
throw new Error("Unsupported stage: " + JSON.stringify(stage));
}
pushDump(dumps) {
dumps.push(this.body);
return dumps;
}
static hashBody(body) {
return object_hash(body, {
algorithm: "md5",
excludeKeys: key => key === "as",
});
}
getUsedFields() {
throw new Error("Cannot be used on base QueryStep class");
}
}
QueryStep.Lookup = class extends QueryStep {
constructor(body) {
const cleared_body = {
from: body.from,
localField: body.localField,
foreignField: body.foreignField,
};
cleared_body.as = QueryStep.hashBody(cleared_body);
super(cleared_body);
this.unwind = body.unwind;
}
hash() {
return this.body.as;
}
pushStage(pipeline) {
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;
}
};
QueryStep.Match = class extends QueryStep {
pushStage(pipeline) {
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 QueryStep.Match(negate_stage(this.body));
}
};
function getAllKeys(obj) {
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;
}, []);
}
module.exports = QueryStep;

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