Difference between revisions of "Find"
m (Markup corrections, presentation improvements, replaced old python library method with mongo shell (find_one -> findOne).) |
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<code>find()</code> is used to filter and project<br/> | <code>find()</code> is used to filter and project<br/> | ||
By default <code>find()</code> returns a cursor containing all the documents in the collection it is used on. This is the same as <code>find({})</code><br /><br/> | By default <code>find()</code> returns a cursor containing all the documents in the collection it is used on. This is the same as <code>find({})</code><br /><br/> | ||
| − | To get all the documents with a certain value, <code>find(<field>:{"$eq":<value>}})</code> can be used, this can be simplified to <code>find(<field>:<value>})</code><br/> | + | To get all the documents with a certain value, <code>find(<field>:{"$eq": <value>}})</code> can be used, this can be simplified to <code>find(<field>: <value>})</code><br/> |
<code>$eq</code> can be replaced with other conditional operators such as <code>$lt</code>, <code>$gt</code> to perform less than or greater than comparisons.<br/><br/> | <code>$eq</code> can be replaced with other conditional operators such as <code>$lt</code>, <code>$gt</code> to perform less than or greater than comparisons.<br/><br/> | ||
To query nested documents, [http://docs.mongodb.org/manual/core/document/#document-dot-notation dot notation] can be used, e.g. <code>parent.child.field</code><br/><br/> | To query nested documents, [http://docs.mongodb.org/manual/core/document/#document-dot-notation dot notation] can be used, e.g. <code>parent.child.field</code><br/><br/> | ||
| − | |||
The second parameter selects what fields to include. If the second parameter is not present the default action is to include all the fields in the result documents.<br/> | The second parameter selects what fields to include. If the second parameter is not present the default action is to include all the fields in the result documents.<br/> | ||
| − | To hide a field, <code><field>:0</code> is used. The other fields won't be removed.<br/> | + | To hide a field, <code><field>: 0</code> is used. The other fields won't be removed.<br/> |
| − | Using <code><field>:1</code> will include that field and hide all the others except the <code>_id</code> and other fields set to 1.<br/> | + | Using <code><field>: 1</code> will include that field and hide all the others except the <code>_id</code> and other fields set to '''1'''.<br/> |
| − | Passing an empty (<code>{}</code>) second parameter hides all fields except the <code>_id</code> field, to hide <code>_id</code> it has to be explicitly set to 0.<br/><br/> | + | Passing an empty (<code>{}</code>) second parameter hides all fields except the <code>_id</code> field, to hide <code>_id</code> it has to be explicitly set to '''0'''.<br/><br/> |
| − | <code> | + | <code>.findOne()</code> limits the result to one document and also applies the <code>.pretty()</code> operation. |
</div> | </div> | ||
| + | |||
<div class="q nonum" data-lang="mongo"> | <div class="q nonum" data-lang="mongo"> | ||
| − | <p class="strong>Show the name and capital for every country of "South America"</p> | + | <p class="strong">Show the name and capital for every country of "South America"</p> |
<pre class=def> | <pre class=def> | ||
| − | db.world.find({continent:"South America"},{"_id":0,name:1,capital:1}) | + | db.world.find( |
| − | </pre> | + | {continent:"South America"}, |
| + | {"_id":0, name:1, capital:1} | ||
| + | )</pre> | ||
</div> | </div> | ||
Revision as of 17:58, 21 March 2018
find() is used to filter and project
By default find() returns a cursor containing all the documents in the collection it is used on. This is the same as find({})
To get all the documents with a certain value, find(<field>:{"$eq": <value>}}) can be used, this can be simplified to find(<field>: <value>})
$eq can be replaced with other conditional operators such as $lt, $gt to perform less than or greater than comparisons.
To query nested documents, dot notation can be used, e.g. parent.child.field
The second parameter selects what fields to include. If the second parameter is not present the default action is to include all the fields in the result documents.
To hide a field, <field>: 0 is used. The other fields won't be removed.
Using <field>: 1 will include that field and hide all the others except the _id and other fields set to 1.
Passing an empty ({}) second parameter hides all fields except the _id field, to hide _id it has to be explicitly set to 0.
.findOne() limits the result to one document and also applies the .pretty() operation.
Show the name and capital for every country of "South America"
db.world.find(
{continent:"South America"},
{"_id":0, name:1, capital:1}
)