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nedb/lib/cursor.js

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/**
* Manage access to data, be it to find, update or remove it
*/
var model = require('./model')
, _ = require('underscore')
;
/**
* Create a new cursor for this collection
* @param {Datastore} db - The datastore this cursor is bound to
* @param {Query} query - The query this cursor will operate on
* @param {Function} execDn - Handler to be executed after cursor has found the results and before the callback passed to find/findOne/update/remove
*/
function Cursor (db, query, execFn) {
this.db = db;
this.query = query || {};
if (execFn) { this.execFn = execFn; }
}
/**
* Set a limit to the number of results
*/
Cursor.prototype.limit = function(limit) {
this._limit = limit;
return this;
};
/**
* Skip a the number of results
*/
Cursor.prototype.skip = function(skip) {
this._skip = skip;
return this;
};
/**
* Sort results of the query
* @param {SortQuery} sortQuery - SortQuery is { field: order }, field can use the dot-notation, order is 1 for ascending and -1 for descending
*/
Cursor.prototype.sort = function(sortQuery) {
this._sort = sortQuery;
return this;
};
/**
* Add the use of a projection
* @param {Object} projection - MongoDB-style projection. {} means take all fields. Then it's { key1: 1, key2: 1 } to take only key1 and key2
* { key1: 0, key2: 0 } to omit only key1 and key2. Except _id, you can't mix takes and omits
*/
Cursor.prototype.projection = function(projection) {
this._projection = projection;
return this;
};
/**
* Apply the projection
*/
Cursor.prototype.project = function (candidates) {
var res = [], self = this
, keepId, action, keys
;
if (this._projection === undefined || Object.keys(this._projection).length === 0) {
return candidates;
}
keepId = this._projection._id === 0 ? false : true;
this._projection = _.omit(this._projection, '_id');
// Check for consistency
keys = Object.keys(this._projection);
keys.forEach(function (k) {
if (action !== undefined && self._projection[k] !== action) { throw new Error("Can't both keep and omit fields except for _id"); }
action = self._projection[k];
});
// Do the actual projection
candidates.forEach(function (candidate) {
var toPush = action === 1 ? _.pick(candidate, keys) : _.omit(candidate, keys);
if (keepId) {
toPush._id = candidate._id;
} else {
delete toPush._id;
}
res.push(toPush);
});
return res;
};
/**
* Get all matching elements
* Will return pointers to matched elements (shallow copies), returning full copies is the role of find or findOne
* This is an internal function, use exec which uses the executor
*
* @param {Function} callback - Signature: err, results
*/
Cursor.prototype._exec = function(callback) {
var candidates = this.db.getCandidates(this.query)
, res = [], added = 0, skipped = 0, self = this
, error = null
, i, keys, key
;
try {
for (i = 0; i < candidates.length; i += 1) {
if (model.match(candidates[i], this.query)) {
// If a sort is defined, wait for the results to be sorted before applying limit and skip
if (!this._sort) {
if (this._skip && this._skip > skipped) {
skipped += 1;
} else {
res.push(candidates[i]);
added += 1;
if (this._limit && this._limit <= added) { break; }
}
} else {
res.push(candidates[i]);
}
}
}
} catch (err) {
return callback(err);
}
// Apply all sorts
if (this._sort) {
keys = Object.keys(this._sort);
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// Sorting
var criteria = [];
for (i = 0; i < keys.length; i++) {
key = keys[i];
criteria.push({ key: key, direction: self._sort[key] });
}
res.sort(function(a, b) {
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var criterion, compare, i;
for (i = 0; i < criteria.length; i++) {
criterion = criteria[i];
compare = criterion.direction * model.compareThings(model.getDotValue(a, criterion.key), model.getDotValue(b, criterion.key), self.db.compareStrings);
if (compare !== 0) {
return compare;
}
}
return 0;
});
// Applying limit and skip
var limit = this._limit || res.length
, skip = this._skip || 0;
res = res.slice(skip, skip + limit);
}
// Apply projection
try {
res = this.project(res);
} catch (e) {
error = e;
res = undefined;
}
if (this.execFn) {
return this.execFn(error, res, callback);
} else {
return callback(error, res);
}
};
Cursor.prototype.exec = function () {
this.db.executor.push({ this: this, fn: this._exec, arguments: arguments });
};
// Interface
module.exports = Cursor;