3. Queries

Query Expansion

Many of the functions in dbee.core claim to expand a query and that abbreviated forms may be used. There are three abbreviated forms, and they are described as follows:

1. nil represents an empty query and is expanded to an empty map
2. A keyword represents a table name and is expanded to a select-all query
3. A parameterless function is a query generator and is expanded to the result of calling the function

Note that maps are not considered abbreviated are equal to their expansion.

The expansion happens in dbee.core/expand-query. This function should be used in query construction functions that you want to be able to accept abbreviated forms.

Common Options

Many of the API functions provided by dbee accept a number of common options. Those options include the following:

• :long-running-threshold

  The number of milliseconds to use as a long-running threshold. If queries exceed this value, a warning will be logged that includes the query and the run time. This value will override any default or configured value.

• :row-fn

  A function that will be executed against every row returned from the database. This value will override any default or configured value.

• :result-set-fn

  A function that will be applied to the entire returned result set.

Transactions

dbee provides a macro dbee.core/with-transaction for executing queries inside of a transaction. The API is similar to that provided by java.jdbc.

Transactions are committed unless they are rolled back using dbee.core/rollback. However, rollback will throw an exception if it is not called from within a transaction. This is to help ensure correctness in transaction code. You may use dbee.core/in-transaction? to determine whether the current execution is occurring within a transaction.

Note that each of these functions will be generated as part of the local database API.

Note: There is a subtle difference between the behavior of with-transaction using the base API and the local database API. Since the base API requires you to provide your own connection for the transaction, the API cannot guarantee that rollback will rollback the outermost transaction when working with embedded transactions. However, the local database API can make this guarantee because with-transaction will use the same connection as the outermost transaction.