Serialize Data to a JSON

PowerSystems.jl supports serializing/deserializing data with JSON. This provides an example of how to write and read a System to/from disk.

Dependencies

Let's use a dataset from the tabular data parsing tutorial:

julia> using PowerSystems
julia> file_dir = joinpath(pkgdir(PowerSystems), "docs", "src", "tutorials", "tutorials_data"); #hide
julia> sys = System(joinpath(file_dir, "case5_re.m"))┌ Error: Matlab parser skipping line number 85 consisting of:
│   };
└ @ PowerSystems ~/work/PowerSystems.jl/PowerSystems.jl/src/parsers/im_io/matlab.jl:64
[ Info: Correcting vm in bus 1 to 1.07762 to match generator set-point
[ Info: Correcting vm in bus 3 to 1.1 to match generator set-point
[ Info: Correcting vm in bus 4 to 1.06414 to match generator set-point
[ Info: Correcting vm in bus 10 to 1.06907 to match generator set-point
[ Info: extending matpower format with data: areas 1x3
[ Info: extending matpower format with data: gen_name 7x4
[ Info: extending matpower format by appending matrix "gen_name" in to "gen"
[ Info: reversing the orientation of branch 6 (4, 3) to be consistent with other parallel branches
[ Info: removing 1 cost terms from generator 5: [1000.0, 0.0]
[ Info: removing 1 cost terms from generator 4: [4000.0, 0.0]
[ Info: removing 3 cost terms from generator 6: Float64[]
[ Info: removing 3 cost terms from generator 7: Float64[]
[ Info: removing 1 cost terms from generator 2: [1500.0, 0.0]
[ Info: removing 1 cost terms from generator 3: [3000.0, 0.0]
[ Info: removing 1 cost terms from generator 1: [1400.0, 0.0]
┌ Info: Constructing System from Power Models
│   data["name"] = "nesta_case5_pjm"
└   data["source_type"] = "matpower"
[ Info: Reading bus data
[ Info: Reading Load data in PowerModels dict to populate System ...
[ Info: Reading LoadZones data in PowerModels dict to populate System ...
[ Info: Reading generator data
[ Info: Reading branch data
[ Info: Reading shunt data
[ Info: Reading DC Line data
[ Info: Reading storage data
System
┌───────────────────┬─────────────┐
│ Property          │ Value       │
├───────────────────┼─────────────┤
│ Name              │             │
│ Description       │             │
│ System Units Base │ SYSTEM_BASE │
│ Base Power        │ 100.0       │
│ Base Frequency    │ 60.0        │
│ Num Components    │ 30          │
└───────────────────┴─────────────┘

Static Components
┌──────────────────────────┬───────┐
│ Type                     │ Count │
├──────────────────────────┼───────┤
│ ACBus                    │ 5     │
│ Arc                      │ 6     │
│ Area                     │ 1     │
│ Line                     │ 5     │
│ LoadZone                 │ 1     │
│ PhaseShiftingTransformer │ 2     │
│ PowerLoad                │ 3     │
│ RenewableDispatch        │ 2     │
│ ThermalStandard          │ 5     │
└──────────────────────────┴───────┘

Write data to a temporary directory

julia> folder = mktempdir();
julia> path = joinpath(folder, "system.json")"/tmp/jl_MYfCth/system.json"
julia> println("Serializing to $path")Serializing to /tmp/jl_MYfCth/system.json
julia> to_json(sys, path)[ Info: Serialized System to /tmp/jl_MYfCth/system.json
[ Info: Serialized System metadata to /tmp/jl_MYfCth/system_metadata.json

Read the JSON file and create a new System

julia> sys2 = System(path)System
┌───────────────────┬─────────────┐
│ Property          │ Value       │
├───────────────────┼─────────────┤
│ Name              │             │
│ Description       │             │
│ System Units Base │ SYSTEM_BASE │
│ Base Power        │ 100.0       │
│ Base Frequency    │ 60.0        │
│ Num Components    │ 30          │
└───────────────────┴─────────────┘

Static Components
┌──────────────────────────┬───────┐
│ Type                     │ Count │
├──────────────────────────┼───────┤
│ ACBus                    │ 5     │
│ Arc                      │ 6     │
│ Area                     │ 1     │
│ Line                     │ 5     │
│ LoadZone                 │ 1     │
│ PhaseShiftingTransformer │ 2     │
│ PowerLoad                │ 3     │
│ RenewableDispatch        │ 2     │
│ ThermalStandard          │ 5     │
└──────────────────────────┴───────┘

How to trouble-shoot serialization issues

If this doesn't work then you likely need to implement custom InfrastructureSystems.serialize and InfrastructureSystems.deserialize methods for your type. Here are some examples of potential problems and solutions:

Problem: Your struct contains a field defined as an abstract type. The deserialization process doesn't know what concrete type to construct.

Solution: Encode the concrete type into the serialized dictionary as a string.

Example: serialize and deserialize methods for DynamicBranch in src/models/dynamic_branch.jl.

Problem: Similar to above in that a field is defined as an abstract type but the struct is parameterized on the actual concrete type.

Solution: Use the fact that the concrete type is encoded into the serialized type of the struct and extract it in a customized deserialze method.

Example: deserialize method for OuterControl in src/models/OuterControl.jl.