JSPM – ngrx-entity-relationship@0.4.1

Package Exports

ngrx-entity-relationship

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Readme

Supports ngrx 8.x and 9.x

Imagine that we have the next entities in ngrx store, every entity is stored in its own feature.

export interface User {
    id: string;
    firstName: string;
    firstLast: string;
    company?: Company;
    companyId?: string;
}

export interface Address {
    id: string;
    street: string;
    city: string;
    country: string;
    company?: Company;
    companyId?: string;
}

export interface Company {
    id: string;
    name: string;
    staff?: Array<User>;
    admin?: User;
    adminId?: string;
    address?: Address;
    addressId?: string;
}

const selectUserState = createFeatureSelector<EntityState<User>>('users');
const selectCompanyState = createFeatureSelector<EntityState<Company>>('companies');
const selectAddressState = createFeatureSelector<EntityState<Address>>('addresses');

store.dispatch(
    setUser({
        user: {
            id: '1',
            firstName: 'John',
            lastName: 'Smith',
            companyId: '1',
        },
    }),
);
store.dispatch(
    setCompany({
        company: {
            id: '1',
            name: 'Magic',
            adminId: '1',
            addressId: '1',
        },
    }),
);
store.dispatch(
    setAddress({
        adress: {
            id: '1',
            street: 'Main st.',
            city: 'Town',
            country: 'Land',
            companyId: '1',
        },
    }),
);

And now we want to get a user with the related company and its address. To have the next structure by the end:

const user = {
    id: '1',
    firstName: 'John',
    lastName: 'Smith',
    companyId: '1',
    company: {
        id: '1',
        name: 'Magic',
        adminId: '2',
        addressId: '1',
        address: {
            id: '1',
            street: 'Main st.',
            city: 'Town',
            country: 'Land',
            companyId: '1',
        },
    },
};

With the default adapter we can select only an entity without its nested entities.

const userAdapter = createEntityAdapter<User>();
const userSelectors = userAdapter.getSelectors();

export const selectUserEntities = createSelector(selectUserState, userSelectors.selectEntities);

store.pipe(
    selectUserEntities,
    map(entities => entities['1']),
);

The solution.

To solve the issue we need rootEntity, relatedEntity and rootEntities from ngrx-entity-relationship.

export const selectUser = rootEntity(
    selectUserState, // selecting our root entity.
    relatedEntity(
        // now we define a relationship we want to add.
        selectCompanyState, // a selector of the related entity.
        'companyId', // the key in the root entity which points to the related entity.
        'company', // the key in the root entity where we'll set the related entity.
        relatedEntity(
            // now we define a relationship we want to add to the company.
            selectAddressState, // a selector of the related entity.
            'addressId', // the key with the id.
            'address', // the key where to set the result.
        ),
    ),
);
export const selectUsers = rootEntities(
    // the same but for a list.
    selectUserState,
    relatedEntity(
        selectCompanyState,
        'companyId',
        'company',
        relatedEntity(selectAddressState, 'addressId', 'address'),
    ),
);

Now we can use the selectors with the store.

this.store.select(selectUser, 'userId');
this.store.select(selectUsers, ['user1', 'user2', 'user3']);

Additional examples.

Of course we can select as many relationships as we want until we have a field with a related id. Check how childrenEntity works. It gathers entities based on a parent field.

export const selectUser = rootEntity(
    selectUserState,
    relatedEntity(
        selectCompanyState,
        'companyId',
        'company',
        childrenEntity(selectUserState, 'companyId', 'staff'),
        relatedEntity(selectUserState, 'adminId', 'admin'),
        relatedEntity(
            selectAddressState,
            'addressId',
            'address',
            relatedEntity(selectCompanyState, 'companyId', 'company'),
        ),
    ),
);

You can simplify the definition with predefined selectors. Check how childrenEntitySelector works. It gathers entities based on a parent field.

const entityUser = rootEntitySelector(selectUserState);
const entityUsers = rootEntitiesSelector(selectUserState);
const entityUserCompany = relatedEntitySelector(selectCompanyState, 'companyId', 'company');
const entityCompanyStaff = childrenEntitySelector(selectUserState, 'companyId', 'staff');
const entityCompanyAdmin = relatedEntitySelector(selectUserState, 'adminId', 'admin');
const entityCompanyAddress = relatedEntitySelector(selectAddressState, 'addressId', 'address');
const entityAddressCompany = relatedEntitySelector(selectCompanyState, 'companyId', 'company');

export const selectUserWithCompany = entityUser(entityUserCompany());
export const selectUserWithStrangePath = entityUser(
    entityUserCompany(
        entityCompanyStaff(),
        entityCompanyAdmin(),
        entityCompanyAddress(entityAddressCompany(entityCompanyAdmin(entityUserCompany(entityCompanyStaff())))),
    ),
);

Transform an entity to a class instance

Every function of the library supports a <T>(entity: T) => T callback. It should be specified as the latest argument, but before relationships definition. The transformation happens before relations.

const entityUser = rootEntitySelector(selectUserState, user => new UserClass(user));

export const selectUser = rootEntity(
    selectUserState,
    user => new UserClass(user),
    relatedEntity(
        selectCompanyState,
        'companyId',
        'company',
        company => new CompanyClass(company),
        childrenEntity(selectUserState, 'companyId', 'staff'),
        relatedEntity(selectUserState, 'adminId', 'admin'),
        relatedEntity(
            selectAddressState,
            'addressId',
            'address',
            relatedEntity(selectCompanyState, 'companyId', 'company'),
        ),
    ),
);

Warnings.

An entity from the same feature with the same id is a different object.

It allows avoiding of circular references.
A selector emits an updated entity only in case if the root or a nested related entity has been updated.
A value of any related key can be undefined.
There's a flag rootEntityFlags.disabled that can be useful to disable selectors during updates of entities. Simply set it to true before you start update and back to false after it.

When you set it to false you need to share the store to get updated entities.

ngrx-entity-relationship