Realm主键约束异常求助：已存在值1/2，常规方案无效

Let's break down what's happening here and fix this issue step by step:

The Root Cause: Mismatched Primary Key Types #

Looking at your code and JSON data, there's a critical mismatch you might have missed:

• Your StationRealm class defines the primary key id as a String type
• But your JSON data provides id as a numeric value (e.g., 1, 2)

Realm handles type conversions silently here, but this creates a hidden problem: when parsing the JSON, Realm stores the numeric id as a numeric type (like Long) instead of a String. This leads to two major issues:

1. When you call realm.clear(StationRealm.class), it might not properly delete entries where the primary key is stored as a numeric type (since your entity class declares it as String).
2. createOrUpdateAllFromJson() can't match the numeric id from JSON to the existing (numeric-stored) primary keys in the database, so it tries to insert a new entry instead of updating—triggering the duplicate key error.

Fixes to Try #

1. Align Primary Key Types (Most Critical) #

You have two options to fix the type mismatch:

Option A: Change Entity Class's id to Numeric Type

Update your StationRealm class to use a numeric primary key that matches the JSON data:

@PrimaryKey
private int id; // Or long if your IDs can be larger than int's limit

This is the simplest fix since your JSON already uses numeric IDs. With this change:

• createOrUpdateAllFromJson() will correctly recognize matching primary keys and update existing entries instead of inserting duplicates.
• realm.clear(StationRealm.class) will properly delete all entries in the table.

Option B: Modify JSON to Use String IDs

If you need to keep the id as a String in your entity class, adjust your JSON data to wrap IDs in quotes:

[{"id":"1","name":"1 - Allen Street", ...}, {"id":"2", ...}]

This ensures Realm parses the id as a String, matching your entity class's definition.

2. Verify Clear/Transaction Logic #

Make sure your clear operation runs inside a valid transaction (which your commented code does). Uncomment that line and add a quick check to confirm the table is actually being cleared:

if (null != realm) {
    try {
        realm.beginTransaction();
        realm.clear(StationRealm.class);
        // Add this log to confirm the table is empty
        long count = realm.where(StationRealm.class).count();
        Log.d(TAG, "After clear, StationRealm count: " + count);
        realm.createOrUpdateAllFromJson(StationRealm.class, json);
        realm.commitTransaction();
        sendStatusRefreshedMessage(context);
    } catch (Exception ex) {
        realm.cancelTransaction();
        Log.e(TAG, "RealmDBStations: " + ex.getMessage());
    }
}

If the count isn't 0 after clearing, you might be working with a different Realm instance or database file.

3. Clean Up Stale Database Data #

If you've been testing with mismatched types, old data might be lingering in the Realm file. To rule this out:

• Uninstall your app from the test device/emulator to delete the existing Realm database.
• Rebuild and re-run your app with the fixed type alignment.

Why Your Previous Fixes Didn't Work #

• realm.clear(): Failed because it was targeting entries with String primary keys, but your existing data had numeric primary keys stored under the same table.
• createOrUpdateAllFromJson(): Couldn't match the numeric JSON IDs to the stored numeric keys (since your entity class declared id as String, Realm didn't recognize them as matching primary keys).

内容的提问来源于stack exchange，提问作者Liru