Android:更改领域迁移中的旧主键 [英] Android: Change old primary key in realm migration

问题描述

我可以在领域迁移脚本中用新的主键更改旧的主键吗?

Can I change old primary key with new primary key in realm migration script?

推荐答案

是的，有可能.

        RealmObjectSchema objectSchema = schema.get("MyObject");
        objectSchema.addField("newId", long.class)
                .transform(new RealmObjectSchema.Function() {
                    @Override
                    public void apply(DynamicRealmObject obj) {
                        obj.setLong("newId", getNewId(obj));
                    }
                })
                .removeField("id")
                .renameField("newId", "id")
                .addPrimaryKey("id");

但是，您不能直接将字段创建为

However, you can't directly create the field as

objectSchema.addField("newId", long.class, FieldAttribute.PRIMARY_KEY)

因为在数据库中将值初始化为0，这意味着您将违反创建的约束.因此，只有在设置了值之后，才必须添加主键约束.

because the values are initialized to 0 in your database, which means you'll be violating the constraint on creation. So you must add the primary key constraint only after the values are set.

就您而言，

RealmObjectSchema objectSchema = schema.get("MyObject");
objectSchema.addField("newId", long.class)
    .transform(new RealmObjectSchema.Function() {
        @Override
        public void apply(DynamicRealmObject obj) {
            obj.setLong("newId", getNewId(obj));
        }
    })
    .removePrimaryKey()
    .addPrimaryKey("newId");

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