insert & read data to mongodb

> use lanzhou
switched to db lanzhou
> db.wuwei.save( { a: 1 } )
WriteResult({ "nInserted" : 1 })
> db.wuwei.find()
{ "_id" : ObjectId("5f0faebe2d6c5971111129df"), "a" : 1 }
> 

e.g.

> db.inventory.insertOne(
...    { item: "canvas", qty: 100, tags: ["cotton"], size: { h: 28, w: 35.5, uom: "cm" } }
... )
{
        "acknowledged" : true,
        "insertedId" : ObjectId("5f0fb0712d6c5971111129e0")
}
> db.inventory.find()
{ "_id" : ObjectId("5f0fb0712d6c5971111129e0"), "item" : "canvas", "qty" : 100, "tags" : [ "cotton" ], "size" : { "h" : 28, "w" : 35.5, "uom" : "cm" } }
> db.inventory.find( { item: "canvas" } )
{ "_id" : ObjectId("5f0fb0712d6c5971111129e0"), "item" : "canvas", "qty" : 100, "tags" : [ "cotton" ], "size" : { "h" : 28, "w" : 35.5, "uom" : "cm" } }
> 
> 
> db.inventory.insertMany([
...    { item: "journal", qty: 25, tags: ["blank", "red"], size: { h: 14, w: 21, uom: "cm" } },
...    { item: "mat", qty: 85, tags: ["gray"], size: { h: 27.9, w: 35.5, uom: "cm" } },
...    { item: "mousepad", qty: 25, tags: ["gel", "blue"], size: { h: 19, w: 22.85, uom: "cm" } }
... ])
{
        "acknowledged" : true,
        "insertedIds" : [
                ObjectId("5f0fb1002d6c5971111129e1"),
                ObjectId("5f0fb1002d6c5971111129e2"),
                ObjectId("5f0fb1002d6c5971111129e3")
        ]
}
> db.inventory.find()
{ "_id" : ObjectId("5f0fb0712d6c5971111129e0"), "item" : "canvas", "qty" : 100, "tags" : [ "cotton" ], "size" : { "h" : 28, "w" : 35.5, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1002d6c5971111129e1"), "item" : "journal", "qty" : 25, "tags" : [ "blank", "red" ], "size" : { "h" : 14, "w" : 21, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1002d6c5971111129e2"), "item" : "mat", "qty" : 85, "tags" : [ "gray" ], "size" : { "h" : 27.9, "w" : 35.5, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1002d6c5971111129e3"), "item" : "mousepad", "qty" : 25, "tags" : [ "gel", "blue" ], "size" : { "h" : 19, "w" : 22.85, "uom" : "cm" } }
> db.inventory.find( { item: "mat" } )
{ "_id" : ObjectId("5f0fb1002d6c5971111129e2"), "item" : "mat", "qty" : 85, "tags" : [ "gray" ], "size" : { "h" : 27.9, "w" : 35.5, "uom" : "cm" } }
> db.inventory.find({item:"mat"})
{ "_id" : ObjectId("5f0fb1002d6c5971111129e2"), "item" : "mat", "qty" : 85, "tags" : [ "gray" ], "size" : { "h" : 27.9, "w" : 35.5, "uom" : "cm" } }
> db.inventory.find({})
{ "_id" : ObjectId("5f0fb0712d6c5971111129e0"), "item" : "canvas", "qty" : 100, "tags" : [ "cotton" ], "size" : { "h" : 28, "w" : 35.5, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1002d6c5971111129e1"), "item" : "journal", "qty" : 25, "tags" : [ "blank", "red" ], "size" : { "h" : 14, "w" : 21, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1002d6c5971111129e2"), "item" : "mat", "qty" : 85, "tags" : [ "gray" ], "size" : { "h" : 27.9, "w" : 35.5, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1002d6c5971111129e3"), "item" : "mousepad", "qty" : 25, "tags" : [ "gel", "blue" ], "size" : { "h" : 19, "w" : 22.85, "uom" : "cm" } }
> db.inventory.insertOne(
...    { item: "canvas", qty: 100, tags: ["cotton"], size: { h: 28, w: 35.5, uom: "cm" } }
... )
{
	"acknowledged" : true,
	"insertedId" : ObjectId("5f0fb1f22d6c5971111129e4")
}
> db.inventory.find({})
{ "_id" : ObjectId("5f0fb0712d6c5971111129e0"), "item" : "canvas", "qty" : 100, "tags" : [ "cotton" ], "size" : { "h" : 28, "w" : 35.5, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1002d6c5971111129e1"), "item" : "journal", "qty" : 25, "tags" : [ "blank", "red" ], "size" : { "h" : 14, "w" : 21, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1002d6c5971111129e2"), "item" : "mat", "qty" : 85, "tags" : [ "gray" ], "size" : { "h" : 27.9, "w" : 35.5, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1002d6c5971111129e3"), "item" : "mousepad", "qty" : 25, "tags" : [ "gel", "blue" ], "size" : { "h" : 19, "w" : 22.85, "uom" : "cm" } }
{ "_id" : ObjectId("5f0fb1f22d6c5971111129e4"), "item" : "canvas", "qty" : 100, "tags" : [ "cotton" ], "size" : { "h" : 28, "w" : 35.5, "uom" : "cm" } }
> 

delete data from mongodb

> db.collection.deleteMany()
2020-07-16T09:58:19.683+0800 E  QUERY    [js] uncaught exception: Error: find() requires query criteria :
Bulk/this.find@src/mongo/shell/bulk_api.js:796:23
DBCollection.prototype.deleteMany@src/mongo/shell/crud_api.js:420:20
@(shell):1:1
> db.inventory.deleteMany()
2020-07-16T09:58:54.991+0800 E  QUERY    [js] uncaught exception: Error: find() requires query criteria :
Bulk/this.find@src/mongo/shell/bulk_api.js:796:23
DBCollection.prototype.deleteMany@src/mongo/shell/crud_api.js:420:20
@(shell):1:1
> db.inventory.deleteMany({})
{ "acknowledged" : true, "deletedCount" : 10 }
> db.inventory.find()
>