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Controller contract anatomy

Dive into into the Tableland controller contract's design.

A controller needs to implement the ITablelandController interface to create a TablelandController contract. This enables advanced, custom access control features. Note that the default controls that allow for the owner to control the table are implemented by the TablelandTables registry contract, so if you don't create your own control, there still are rules applied.

interface ITablelandController {
    /**
     * @dev Object defining how a table can be accessed.
     */
    struct Policy {
        bool allowInsert;
        bool allowUpdate;
        bool allowDelete;
        string whereClause;
        string withCheck;
        string[] updatableColumns;
    }

    /**
     * @dev Returns a {Policy} struct defining how a table can be accessed by `caller`.
     */
    function getPolicy(address caller) external payable returns (Policy memory);
}

Policy​

Object defining how a table can be accessed.

allowInsert (boolean)

Whether or not the table should allow SQL INSERT statements.

allowUpdate (boolean)

Whether or not the table should allow SQL UPDATE statements.

allowDelete (boolean)

Whether or not the table should allow SQL DELETE statements.

whereClause (string)

A conditional WHERE clause used with SQL UPDATE and DELETE statements.

  • For example, a value of "foo > 0" will concatenate all SQL UPDATE and/or DELETE statements with "WHERE foo > 0". This can be useful for limiting how a table can be modified.
  • Use the Policies library’s joinClauses to include more than one condition.

withCheck (string)

A conditional CHECK clause used with SQL INSERT statements.

  • For example, a value of "foo > 0" will concatenate all SQL INSERT statements with a check on the incoming data. Namely, "CHECK (foo > 0)". This can be useful for limiting how table data ban be added.
  • Use the Policies library’s joinClauses to include more than one condition.

updatableColumns (string[])

A list of SQL column names that can be updated.

getPolicy​

Returns a Policy struct, defining how a table can be accessed by caller.

Parameters​

caller (address) The address to be used to check access control permissions.

Definition​

external, payable

Returns​

Policy The corresponding Policy struct for the given address.

Note: The method is marked as payable. This means developers can set up access controls that require payment in order for the caller to even make a write query attempt.