如何使用 Xodus DNQ 检查组合的唯一性

Question

我有两个实体； municipality 和 city。市政当局被假定具有唯一的名称，而城市被假定为在其自治市内是唯一的。

有没有一种方法可以为城市设置一个约束，使其名称和城市名称的组合必须是唯一的？

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实体

class XdCity(entity: Entity) : XdEntity(entity) {
    companion object : XdNaturalEntityType<XdCity>()

    var name by xdRequiredStringProp()
    var municipality: XdMunicipality by xdLink1(
        XdMunicipality::cities,
        onDelete = OnDeletePolicy.CLEAR,
        onTargetDelete = OnDeletePolicy.CASCADE
    )
}

class XdMunicipality(entity: Entity) : XdEntity(entity) {
    companion object : XdNaturalEntityType<XdMunicipality>()

    var name by xdRequiredStringProp(unique = true)
    val cities by xdLink1_N(
        XdCity::municipality,
        onDelete = OnDeletePolicy.CASCADE,
        onTargetDelete = OnDeletePolicy.CLEAR
    )
}

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测试用例

@Test
fun testAddSameCityName() {
    Database.store.transactional {
        val municipality = XdMunicipality.new("Mun 1")
        val city = XdCity.new("City")
        city.municipality = municipality
    }

    // Allow insertion of same city name in other municipality
    Database.store.transactional {
        val municipality = XdMunicipality.new("Mun 2")
        val city = XdCity.new("City")
        city.municipality = municipality
    }

    // Do not allow insertion of existing city name in municipality
    assertFailsWith<ConstraintsValidationException> {
        Database.store.transactional {
            val municipality = XdMunicipality.find("Mun 1")
            val city = XdCity.new("City")
            city.municipality = municipality
        }
    }
}

Answer 1

建议的方法是在 XdCity 和 XdMunicipality 之间使用 xdParent 和 xdChildren 关系。

当数据库有历史时，改变关系可能不是那么容易。要解决市政范围内唯一名称的问题，您可以对实体类型使用复合索引，如下所示：

        companion object : XdNaturalEntityType<XdCity>() {
            override val compositeIndices = listOf(
                    listOf(XdCity:: municipality, ...may goes anything like XdCity::name)
            )
        }