Expression Types

In the SDK, these predicate expressions are given the TypeScript type Expression, and we can see that there are several different types of expression. These are all expression types which can be used in the where clause of a query our query function will need to handle them via the fetch_rows function.

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export type Expression = {
    expressions: Expression[];
    type: "and";
} | {
    expressions: Expression[];
    type: "or";
} | {
    expression: Expression;
    type: "not";
} | {
    column: ComparisonTarget;
    operator: UnaryComparisonOperator;
    type: "unary_comparison_operator";
} | {
    column: ComparisonTarget;
    operator: BinaryComparisonOperator;
    type: "binary_comparison_operator";
    value: ComparisonValue;
} | {
    column: ComparisonTarget;
    operator: BinaryArrayComparisonOperator;
    type: "binary_array_comparison_operator";
    values: ComparisonValue[];
} | {
    in_collection: ExistsInCollection;
    type: "exists";
    where: Expression;
};

There are logical expressions like and, or, and not, which serve to combine other simpler expressions.

There are unary (eg: NULL, IS NOT NULL, etc...) and binary (eg: = (equal), != (not-equal), > (greater-than), < (less-than), >= (greater-or-equal)) comparison operator expressions.

And there are exists expressions, which are expressed using a sub-query against another collection.

For now, we'll concentrate on logical expressions and comparison operator expressions.

Let's begin to construct the where clause in the next section.