# Announce: A different way to read JSON data, LazyJSON.jl

**URL:** <https://discourse.julialang.org/t/announce-a-different-way-to-read-json-data-lazyjson-jl/9046>\
**Category:** Data\
**Created:** [February 14, 2018, 2:09am UTC](https://discourse.julialang.org/t/announce-a-different-way-to-read-json-data-lazyjson-jl/9046 "2018-02-14T02:09:24Z")\
**Posts on this page:** 1\
**Showing post:** 9

<div class="post-metadata">

**Author:** ![samoconnor](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/samoconnor/32/1802_2.png) [@samoconnor](https://discourse.julialang.org/u/samoconnor)\
**Post date:** [February 22, 2018, 1:39pm UTC](https://discourse.julialang.org/t/announce-a-different-way-to-read-json-data-lazyjson-jl/9046/9 "2018-02-22T13:39:06Z")

</div>

About `LazyJSON.splice`:

So, I was thinking about how LazyJSON should do updates.  
Since it returns `AbstractDict`, you can already use `Base.merge` to create a modified `Dict`, but that has about the same overhead as JSON.jl.

However, there is an update use case where LazyJOSN can do quite well: you have a largish JSON text and you need to update a few values. `LazyJSON.splice` works entirely in the text string domain and requires only a few lines of code (currently only replacing values is supported, but inserting new values is possible too):

```julia
splice(j::JSON.Value, v::JSON.Value, x) = value(splice(j.s, v.i, x, j.i))

splice(s::AbstractString, i::Int, x, start_i = 1) = 
    string(SubString(s, start_i, i - 1),
           jsonstring(x),
           SubString(s, lastindex_of_value(s, i) + 1))

```

e.g.

```julia
j = """{
    "id": 1296269,
    "owner": {
        "login": "octocat"
    },
    "parent": {
        "name": "test-parent"
    }
}"""

@test LazyJSON.splice(j, ["owner", "login"], "foo") ==
"""{
    "id": 1296269,
    "owner": {
        "login": "foo"
    },
    "parent": {
        "name": "test-parent"
    }
}"""

@test LazyJSON.splice(j, ["owner"], "foo") ==
"""{
    "id": 1296269,
    "owner": "foo",
    "parent": {
        "name": "test-parent"
    }
}"""

j = LazyJSON.value(j)

LazyJSON.splice(j, j.owner.login, "foo")
LazyJSON.Object with 3 entries:
  "id" => 1296269
  "owner" => LazyJSON.Object("login"=>"foo")
  "parent" => LazyJSON.Object("name"=>"test-parent")

```

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