DML

The Ur/Web library also includes an embedding of a fragment of SQL's DML, the Data Manipulation Language, for modifying database tables. Any piece of DML may be executed in a transaction.

$$\begin{array}{l} \mathsf{type} \; \mathsf{dml} \\ \mathsf{... ...thsf{dml} \to \mathsf{transaction} \; \mathsf{unit} \end{array}$$

The function $\mathsf{Basis.dml}$ will trigger a fatal application error if the command fails, for instance, because a data integrity constraint is violated. An alternate function returns an error message as a string instead.

$$\begin{array}{l} \mathsf{val} \; \mathsf{tryDml} : \mathsf{d... ...ransaction} \; (\mathsf{option} \; \mathsf{string}) \end{array}$$

Properly typed records may be used to form $\mathsf{INSERT}$ commands.

$$\begin{array}{l} \mathsf{val} \; \mathsf{insert} : \mathsf{f... ...] \; [] \; []) \; \mathsf{fields}) \to \mathsf{dml} \end{array}$$

An $\mathsf{UPDATE}$ command is formed from a choice of which table fields to leave alone and which to change, along with an expression to use to compute the new value of each changed field and a $\mathsf{WHERE}$ clause. Note that, in the table environment applied to expressions, the table being updated is hardcoded at the name $\mathsf{T}$ . The parsing extension for $\mathsf{UPDATE}$ will elaborate all table-free field references to use table variable $\mathsf{T}$ .

$$\begin{array}{l} \mathsf{val} \; \mathsf{update} : \mathsf{u... ...ged}] \; [] \; [] \; \mathsf{bool} \to \mathsf{dml} \end{array}$$

A $\mathsf{DELETE}$ command is formed from a table and a $\mathsf{WHERE}$ clause. The above use of $\mathsf{T}$ is repeated.

$$\begin{array}{l} \mathsf{val} \; \mathsf{delete} : \mathsf{f... ...lds}] \; [] \; [] \; \mathsf{bool} \to \mathsf{dml} \end{array}$$