JSON persistence

How to persist data using a JSON file.

Key takeaways

JsonFilePersister	Component in the data module, persistence library used to persist data in JSON format.
configure	Method used to pass the path to a JSON file.
save	Method used to save data to a JSON file.
load	Method used to extract data from a JSON file.

Introduction

This tutorial will help you understand how to create a JSON persistence component. It starts by explaining the pre-requisites. Then it continues with an explanation on how to create a JSON persistence object, save data to it, and extract stored data from it. In the end, it provides an example where all the explained methods are included.

Persisting data in a JSON file

Pre-requisites

In order to create a JSON persistence component, we need to import the JsonFilePersister class. This class belongs to the persistence library in the data module. To include this class use the following command:

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import (
	persist "github.com/pip-services4/pip-services4-go/pip-services4-persistence-go/persistence"
)

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from pip_services4_persistence.persistence import JsonFilePersister

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Creating the JSON persistence component

There are two ways to create a JSON persistence component. The first consists of declaring an instance of the JsonFilePersister class and passing the JSON file’s path to the constructor. Our code will be as follows:

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import (
	persist "github.com/pip-services4/pip-services4-go/pip-services4-persistence-go/persistence"
)

persister := persist.NewJsonFilePersister[any]("./data.json")

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from pip_services4_persistence.persistence import JsonFilePersister

persister = JsonFilePersister("data.json")

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The second uses a config object to define the JSON file path. In this case, we need to define a ConfigParams object with the path and use the configure method to pass this object to the JSON persistence object.

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import (
	"context"

	config "github.com/pip-services4/pip-services4-go/pip-services4-components-go/config"
	persist "github.com/pip-services4/pip-services4-go/pip-services4-persistence-go/persistence"
)

persister := persist.NewJsonFilePersister[any]("")
myConfig := config.NewConfigParamsFromTuples("path", "./data.json")
persister.Configure(context.Background(), myConfig)

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from pip_services4_persistence.persistence import JsonFilePersister
from pip_services4_components.config import ConfigParams

persister = JsonFilePersister()
my_config = ConfigParams.from_tuples("path", "data.json")
persister.configure(my_config)

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Saving data on a JSON file

To store data in a JSON file we use the save method. The first parameter is the trace_id, which is used to trace execution through the call chain. The second one is the JSON value we want to save. The following example shows how to use it.

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persister.Save(context.Background(), []interface{}{"A1", "B1", "C1"})

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persister.save(None, ["A1", "B1", "C1"])

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Loading data from a JSON file

To load data from a JSON file we use the load method, which returns the loaded items. This method has the trace_id parameter as input. The code below explains its usage.

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items, _ := persister.Load(context.Background())

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items = persister.load(None)

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Example

In the following example, we put everything together. First, we create a JSON persistence object, then we save some data to the JSON file, and lastly, we extract the stored data from the JSON file.

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import (
	"context"
	"fmt"

	persist "github.com/pip-services4/pip-services4-go/pip-services4-persistence-go/persistence"
)

// Create the JSON persistence component
persister := persist.NewJsonFilePersister[any]("./data.json")
// Save data on the JSON persistence object
persister.Save(context.Background(), []interface{}{"A1", "B1", "C1"})
// Read data from the JSON persistence object
items, _ := persister.Load(context.Background())

fmt.Print(items)

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from pip_services4_persistence.persistence import JsonFilePersister

# Create the JSON persistence component
persister = JsonFilePersister("data.json")

# Save data on the JSON persistence object
persister.save("123", ["A", "B", "C"])

# Read data from the JSON persistence object
items = persister.load("123")
print(items)

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After running it, our output will be:

And, our data.json file will contain:

Wrapping up

In this tutorial, we have learned how to persist data and how to extract persisted data from a JSON file. In the end, we saw an example that summarizes all JSON persistence operations.