e1464fd317
Fixes https://github.com/docker/distribution/issues/3097 Signed-off-by: Yong Wen Chua <lawliet89@users.noreply.github.com>
88 lines
2.9 KiB
Markdown
88 lines
2.9 KiB
Markdown
# go-jmespath - A JMESPath implementation in Go
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[](https://travis-ci.org/jmespath/go-jmespath)
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go-jmespath is a GO implementation of JMESPath,
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which is a query language for JSON. It will take a JSON
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document and transform it into another JSON document
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through a JMESPath expression.
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Using go-jmespath is really easy. There's a single function
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you use, `jmespath.search`:
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```go
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> import "github.com/jmespath/go-jmespath"
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>
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> var jsondata = []byte(`{"foo": {"bar": {"baz": [0, 1, 2, 3, 4]}}}`) // your data
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> var data interface{}
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> err := json.Unmarshal(jsondata, &data)
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> result, err := jmespath.Search("foo.bar.baz[2]", data)
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result = 2
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```
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In the example we gave the ``search`` function input data of
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`{"foo": {"bar": {"baz": [0, 1, 2, 3, 4]}}}` as well as the JMESPath
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expression `foo.bar.baz[2]`, and the `search` function evaluated
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the expression against the input data to produce the result ``2``.
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The JMESPath language can do a lot more than select an element
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from a list. Here are a few more examples:
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```go
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> var jsondata = []byte(`{"foo": {"bar": {"baz": [0, 1, 2, 3, 4]}}}`) // your data
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> var data interface{}
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> err := json.Unmarshal(jsondata, &data)
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> result, err := jmespath.search("foo.bar", data)
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result = { "baz": [ 0, 1, 2, 3, 4 ] }
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> var jsondata = []byte(`{"foo": [{"first": "a", "last": "b"},
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{"first": "c", "last": "d"}]}`) // your data
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> var data interface{}
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> err := json.Unmarshal(jsondata, &data)
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> result, err := jmespath.search({"foo[*].first", data)
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result [ 'a', 'c' ]
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> var jsondata = []byte(`{"foo": [{"age": 20}, {"age": 25},
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{"age": 30}, {"age": 35},
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{"age": 40}]}`) // your data
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> var data interface{}
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> err := json.Unmarshal(jsondata, &data)
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> result, err := jmespath.search("foo[?age > `30`]")
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result = [ { age: 35 }, { age: 40 } ]
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```
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You can also pre-compile your query. This is usefull if
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you are going to run multiple searches with it:
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```go
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> var jsondata = []byte(`{"foo": "bar"}`)
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> var data interface{}
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> err := json.Unmarshal(jsondata, &data)
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> precompiled, err := Compile("foo")
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> if err != nil{
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> // ... handle the error
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> }
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> result, err := precompiled.Search(data)
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result = "bar"
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```
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## More Resources
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The example above only show a small amount of what
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a JMESPath expression can do. If you want to take a
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tour of the language, the *best* place to go is the
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[JMESPath Tutorial](http://jmespath.org/tutorial.html).
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One of the best things about JMESPath is that it is
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implemented in many different programming languages including
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python, ruby, php, lua, etc. To see a complete list of libraries,
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check out the [JMESPath libraries page](http://jmespath.org/libraries.html).
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And finally, the full JMESPath specification can be found
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on the [JMESPath site](http://jmespath.org/specification.html).
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