TYPEORM Error: Attempting to access the 'length' property of an undefined entity is not possible

I successfully established a connection to an Azure Database, but encountered an error when attempting to create tables. The server failed with the following message:

[path]/node_modules/typeorm/driver/sqlserver/SqlServerQueryRunner.js:2309
                        if (!dbTables.length)
                                      ^

TypeError: Cannot read properties of undefined (reading 'length')
    at SqlServerQueryRunner.<anonymous> ([path]/node_modules/typeorm/driver/sqlserver/SqlServerQueryRunner.js:2309:39)
    at step ([path]/node_modules/tslib/tslib.js:143:27)
    at Object.next ([path]/node_modules/tslib/tslib.js:124:57)
    at fulfilled ([path]/node_modules/tslib/tslib.js:114:62)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)

Despite my efforts to find a solution, I have not been successful. Any assistance you could provide would be greatly appreciated.

javascriptdatabasetypescriptazuretypeorm

Answer №1

The variable dbTables is not defined in your code. The compiler didn't catch this earlier because you relied on the non-null assertion operator (exclamation point: !).

To enhance your program's behavior, consider checking if the variable is defined first, like this:

// check first if variable is defined
if (dbTables && dbTables.length) {}

You could also use a shorter version of the check:

if (dbTables?.length) {}

This situation demonstrates why overusing the non-null assertion operator can be risky for your codebase. It should only be used when you have better knowledge of types than the compiler, which is rare.

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