Custom or override join in Sequelize.js

问题

I need to create a custom join condition using Sequelize.js with MSSQL. Specifically, I need to join TableB based on a COALESCE value from columns in TableA and TableB and end up with a join condition like this:

LEFT OUTER JOIN [TableB]
    ON [TableB].[ColumnB] = COALESCE (
        [TableC].[ColumnC],
        [TableA].[ColumnA]
    )

I'd settle for an OR clause in my join:

LEFT OUTER JOIN [TableB]
    ON [TableB].[ColumnB] = [TableA].[ColumnA]
    OR [TableB].[ColumnB] = [TableC].[ColumnC]

I read that you can achieve behaviour like this by including required: false in your scope definition. As you can see, I've plastered my scope with it attempting to get this to work.

The best I could get is this (note the AND clause):

LEFT OUTER JOIN [TableB]
    ON [TableB].[ColumnB] = [TableA].[ColumnA]
    AND [TableB].[ColumnB] = COALESCE (
        [TableC].[ColumnC],
        [TableA].[ColumnA]
    )

If I were using MySQL, I think I could simply use the COALESCE value from the SELECT in the JOIN and be good to go but in my prior research read that it was required to recalculate the value.

I've included a stripped down model definition for TableA:

export default (sequelize, DataTypes) => sequelize.define('TableA',
    {
        // Attributes omitted..
    },
    {
        classMethods: {
            associate ({
                TableB,
                TableC
            }) {
                this.belongsTo(TableB, {
                    foreignKey: 'ColumnA',
                    targetKey: 'ColumnB'
                });

                this.belongsTo(TableC, {
                    foreignKey: 'ColumnA',
                    targetKey: 'ColumnC'
                });
            },
            attachScope ({
                TableB,
                TableC
            }) {
                this.addScope('defaultScope', {
                    attributes: [
                        ...Object.keys(this.attributes),
                        [
                            sequelize.fn(
                                'COALESCE',
                                sequelize.col('[TableC].[ColumnC]'),
                                sequelize.col('[TableA].[ColumnA]')
                            ),
                            'ColumnA'
                        ]
                    ],
                    include: [
                        {
                            model: TableB,
                            where: {
                                ColumnB: sequelize.fn(
                                    'COALESCE',
                                    sequelize.col('[TableC].[ColumnC]'),
                                    sequelize.col('[TableA].[ColumnA]')
                                )
                            },
                            required: false
                        },
                        {
                            model: TableC,
                            required: false
                        }
                    ],
                    required: false
                }, { override: true });
            }
        }
    }
);

Any assistance would be greatly appreciated, and if any additional information is required please let me know.

Note: I'm working with a legacy database and unfortunately cannot change the data structure.

回答1:

Hi I had the same issue and finally I solved using a SQL pure query.

Example:

const query = `SELECT s.*, us.UserId \
                FROM UserSections AS us \
                RIGHT JOIN Sections AS s ON (s.id = us.SectionId) \
                WHERE s.parentId = ${sectionId}`;

return db.query(query, { type: db.QueryTypes.SELECT });

The problem is that this function will return a IMyType instead of IMyTypeInstance

Can it works for you??

来源：https://stackoverflow.com/questions/41467135/custom-or-override-join-in-sequelize-js

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sequelize.js