MongoDB journey (4) Deep Learning

MongoDB Tour (4) In-depth study of Postedon ------------------------------------------------------ tips: SKU: StockkeepingUnit, minimum inventory unit. Db. categories. find ({_ id: {$ in: product [category_ids]}); db. products. renameCollection (store_produc

MongoDB Tour (4) In-depth study of Posted on ------------------------------------------------------ tips: SKU: Stock keeping Unit, minimum inventory Unit. Db. categories. find ({_ id: {$ in: product ['category _ id']}); db. products. renameCollection ("store_produc

MongoDB journey (4) deep learning about Posted on

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Tips:

SKU: Stock keeping Unit, U.S. server, minimum inventory Unit.

Db. categories. find ({_ id: {$ in: product ['category _ id']});

Db. products. renameCollection ("store_products ");

Db. createCollection ("users. actions", {capped: true, size: 1024 });

Db. user. actions. find (). sort ({"$ natural":-1 });

Db. system. namespaces. find (); db. system. indexes. find ();

In MongoDBV2.0, The BSON document size is limited to 16 MB. It is easy to design a good data model; performance is related.

Db. products. find ({'slug': 'Wheel-barrow-9092 '}); = like query in SQL

Db. users. find ({first_name: "Smith", age: 40}); and query

Db. users. find ({age: {$ gte: 0}, age: {$ lte: 30}); db. users. find ({age :{$ gte: 0, $ lte30 }});

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Others:

Set operators: $ in, $ all, $ nin;

Boolean operator: $ ne, $ not, $ or, $ and, $ exits;

The above should be enough for daily use; there are some more in-depth query methods, and we will not continue to introduce them here.

I will introduce the projection technology more:

Db. users. find ({},{ username: 1}); // The returned result contains only two fields: _ id and username;

Db. users. find ({},{ addresses: 0, payment_methods: 0}); // The returned result set object does not contain the addresses and payment_methodsfields.

Db. products. find ({},{ reviews: {$ slice: 12 }}); // the first 12 articles in the comments are returned.

Db. products. find ({},{ reviews :{$ slice:-5 }}); // The last five articles in the comments returned

Db. products. find ({},{ reviews :{$ slice: [24,12] }}); // skip the first 24 and then 12 articles

In sort,-1 is in descending order, and 1 is in ascending order.

Db. products. distinct ("tag ");

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Aggregate command: group function; map-reduce function;

Atomic document processing: MongoDB without transactions provides an atomic method to process the document: findAndModify command.

Db. products. update ({price: {$ lte: 10 },{$ addToSet: {tags: 'cheap '}); // basically, the update operator is the prefix, the query operator is usually an infix.

Upsert: No insert, no record filing space, update exists, limited to one record.

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Based on the current situation, website space, mongoDB indexing, replication, sharding, and deployment, we will not discuss it for the moment. Take a break!