Go语言中mgo存储math/big.Rat高精度小数的策略

package main

import (
    "fmt"
    "math/big"
    "log"

    "go.mongodb.org/mongo-driver/bson" // 使用新的go.mongodb.org/mongo-driver
    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
    "context"
    "time"
)

// CurrencyValue 用于在MongoDB中存储big.Rat的自定义结构体
type CurrencyValue struct {
    Num   int64 `bson:"num"`   // 分子
    Denom int64 `bson:"denom"` // 分母
}

// CustomTest 包含CurrencyValue的测试结构
type CustomTest struct {
    ID     string        `bson:"_id,omitempty"`
    Budget CurrencyValue `bson:"budget"`
}

// ToBigRat 将CurrencyValue转换为*big.Rat
func (cv *CurrencyValue) ToBigRat() *big.Rat {
    return big.NewRat(cv.Num, cv.Denom)
}

// FromBigRat 将*big.Rat转换为CurrencyValue
func FromBigRat(r *big.Rat) CurrencyValue {
    // 获取分子和分母的big.Int值
    numBigInt := r.Num()
    denomBigInt := r.Denom()

    // 转换为int64。如果超出int64范围，这里需要额外的错误处理或选择其他存储方式（如string）
    if !numBigInt.IsInt64() || !denomBigInt.IsInt64() {
        log.Fatalf("Error: big.Rat numerator or denominator exceeds int64 range. Num: %s, Denom: %s", numBigInt.String(), denomBigInt.String())
    }

    return CurrencyValue{
        Num:   numBigInt.Int64(),
        Denom: denomBigInt.Int64(),
    }
}

func main() {
    ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
    defer cancel()

    client, err := mongo.Connect(ctx, options.Client().ApplyURI("mongodb://localhost:27017"))
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err = client.Disconnect(ctx); err != nil {
            log.Fatal(err)
        }
    }()

    collection := client.Database("db_log").Collection("test_precision")

    // 1. 创建一个big.Rat实例
    initialRat := big.NewRat(5, 10) // 0.5
    fmt.Printf("Initial big.Rat: %s (FloatString: %s)\n", initialRat.String(), initialRat.FloatString(10))

    // 2. 将big.Rat转换为CurrencyValue
    cvToStore := FromBigRat(initialRat)

    // 3. 创建CustomTest对象并存储
    testDoc := CustomTest{
        ID:     "initial_budget",
        Budget: cvToStore,
    }

    _, err = collection.InsertOne(ctx, testDoc)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println("Initial budget stored successfully.")

    // 演示更新操作，模拟多次减法
    cmp := big.NewRat(1, 100000) // 0.00001
    currentRat := initialRat // 从初始值开始

    for i := 0; i < 20; i++ {
        currentRat.Sub(currentRat, cmp)
        fmt.Printf("Iteration %d: %s (FloatString: %s)\n", i+1, currentRat.String(), currentRat.FloatString(10))
    }

    // 4. 存储更新后的big.Rat
    cvUpdatedToStore := FromBigRat(currentRat)
    updatedDoc := CustomTest{
        ID:     "updated_budget",
        Budget: cvUpdatedToStore,
    }
    _, err = collection.InsertOne(ctx, updatedDoc)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println("Updated budget stored successfully.")

    // ... (读取流程将在下一节展示)
}

func main() {
    // ... (连接MongoDB，存储数据部分同上) ...

    collection := client.Database("db_log").Collection("test_precision")

    // 5. 从MongoDB读取数据
    fmt.Println("\n--- Reading data from MongoDB ---")

    // 读取初始预算
    var retrievedInitial CustomTest
    err = collection.FindOne(ctx, bson.M{"_id": "initial_budget"}).Decode(&retrievedInitial)
    if err != nil {
        log.Fatal(err)
    }
    initialBudgetRat := retrievedInitial.Budget.ToBigRat()
    fmt.Printf("Retrieved initial budget: %s (FloatString: %s)\n", initialBudgetRat.String(), initialBudgetRat.FloatString(10))

    // 读取更新后的预算
    var retrievedUpdated CustomTest
    err = collection.FindOne(ctx, bson.M{"_id": "updated_budget"}).Decode(&retrievedUpdated)
    if err != nil {
        log.Fatal(err)
    }
    updatedBudgetRat := retrievedUpdated.Budget.ToBigRat()
    fmt.Printf("Retrieved updated budget: %s (FloatString: %s)\n", updatedBudgetRat.String(), updatedBudgetRat.FloatString(10))

    // 验证精度
    expectedFinalRat := big.NewRat(5, 10) // 0.5
    cmp := big.NewRat(1, 100000) // 0.00001
    for i := 0; i < 20; i++ {
        expectedFinalRat.Sub(expectedFinalRat, cmp)
    }
    fmt.Printf("Expected final budget (recalculated): %s (FloatString: %s)\n", expectedFinalRat.String(), expectedFinalRat.FloatString(10))

    if expectedFinalRat.Cmp(updatedBudgetRat) == 0 {
        fmt.Println("Precision check passed: Retrieved updated budget matches recalculated expected value.")
    } else {
        fmt.Println("Precision check FAILED: Retrieved updated budget does NOT match recalculated expected value.")
    }
}