> Full SurrealDB documentation index: https://surrealdb.com/docs/llms.txt

# Regex

models.Regex in the Go SDK for the SurrealDB 4.0 regex kind: a pattern in Rust regex syntax, sending a regex as a query variable to match strings, String and SurrealString, why a *regexp.Regexp is refused, and why servers before 4.0 cannot receive a regex.

A `models.Regex` holds the text of a regular expression for the SurrealDB `regex` kind. SurrealDB compiles a regex with the syntax of the Rust `regex` crate, not with Go's `regexp` package. The SDK therefore keeps the pattern as text and never compiles it. This page documents the type and when you can send a regex. Sending a `Regex` needs SurrealDB 4.0.

**Package:** `github.com/surrealdb/surrealdb.go/v2/pkg/models`

**Source:** [pkg/models/regex.go](https://github.com/surrealdb/surrealdb.go/blob/main/pkg/models/regex.go)

---

## Definition {#definition}

```go
type Regex struct {
	Pattern string
}
```

`Pattern` is the text of the regex, without the slashes around it. The zero value is the empty pattern, which matches any text.

---

## Matching in a query {#matching}

Send a `Regex` as a query variable, and use the SurrealQL `=` operator to compare a string with it. With a regex, `=` checks whether the string matches the pattern:

```go
results, err := surrealdb.Query[[]string](ctx, db,
	"SELECT VALUE name FROM person WHERE name = $pattern",
	map[string]any{"pattern": models.Regex{Pattern: "^[A-J]"}},
)
```

A regex that the server returns, such as one stored in a field, decodes into a `Regex`, including from `any`.

---

## Methods {#methods}

### `.String()` {#string}

Returns the regex as the server writes it: the pattern between slashes, with each slash in it escaped, as in `/a\/b/`.

**Returns:** `string`

### `.SurrealString()` {#surrealstring}

Returns the regex as a SurrealQL literal, such as `/a+/`. It escapes each slash that the pattern does not escape already. For the empty pattern, it writes a cast of the empty string instead, because `//` starts a comment in SurrealQL.

**Returns:** `string`

```go
path := models.Regex{Pattern: "^/api/v[0-9]+/"}
fmt.Println(path.SurrealString())
```

```text title="Output"
/^\/api\/v[0-9]+\//
```

Send a regex as a variable rather than writing its literal into a query.

---

## Rust syntax and Go's regexp {#go-regexp}

The Rust syntax is close to the RE2 syntax of Go's `regexp`, but not the same. In Rust, `\d`, `\w`, `\s` and `\b` match Unicode text, while in Go they match ASCII only. The class set operations of Rust, such as `[a-z&&[^aeiou]]`, mean something else in Go. `regexp.Compile(r.Pattern)` gives Go's reading of a pattern, which can differ from the server's.

For this reason, the SDK never converts a `*regexp.Regexp` into a `Regex` or back. Sending a `regexp.Regexp` or a `*regexp.Regexp` fails with the error `cannot encode a *regexp.Regexp, as Go's regular expression syntax is not SurrealQL's: use models.Regex`.

---

## Servers before SurrealDB 4.0 {#earlier-servers}

Plain CBOR, which servers before 4.0 speak, has no form for a regex. Encoding a `Regex` for plain CBOR fails with an error that wraps `constants.ErrNeedsCBOR2`, and the SDK sends nothing:

```text title="Error output with SurrealDB 3.x"
cborwire: a regex (CBOR tag 193) has no plain CBOR form: the value can only be sent over cbor.2
```

To match on an earlier server, send the pattern as a string and cast it in the query. This works on both SurrealDB 3.x and 4.0:

```go
results, err := surrealdb.Query[bool](ctx, db, "RETURN $name = <regex>$pattern", map[string]any{
	"name":    "tobie",
	"pattern": "^[a-z]+$",
})
```

An HTTP connection sends plain CBOR until the server answers it in cbor.2. A `Regex` in the first request of a new HTTP connection therefore fails, even with SurrealDB 4.0. Connect with `WithVersionCheck(true)`, or sign in first, so that the connection uses cbor.2 from the start.

---

## See also

- [Value types](/docs/reference/golang/concepts/value-types.md#regular-expressions) for how values convert
- [Regex](/docs/reference/query-language/language-primitives/data-types/regex.md) for the SurrealQL kind